Back when I was just starting out on my own, I shared an apartment with Sarah. She was a petite redhead with small perky tits, and a wicked sense of humour. We got on really well with each other and used to go out drinking and dancing most weekends.

Pretty early on, Sarah dared me to 'go commando' on one of our nights out, saying "if you do it, I will too". For those who don't know, for us that meant wearing a short skirt or dress, with nothing underneath. That quickly became our "thing". Before leaving the house, one of us would tell out "panty check!" and the other would flash them quickly as proof. It was harmless fun and added a little spice to the night.

Events took a turn when, after another night on the town we were stood in the queue for some takeaway food and Sarah shouted it out "Panty check!" My alcohol-fogged brain reacted and I flashed her. Along with everyone who had turned around to see what the noise was. From that moment I started planning my revenge.

My opportunity came at a friend's birthday a couple of weeks later. We went out for a meal to celebrate, and if course Sarah and I both went commando. Towards the end of the night, I gave the waiter my phone and asked him to take a group photo. I put my arm around Sarah's waist and as he pressed the button I sneakily lifted the hem of her skirt.

My plan worked perfectly. She hadn't noticed what I'd done and when I checked the photo her bright red bush was on full display. The following morning I carefully cropped the image to protect her modesty and posted it to social media. I waited an hour or two, then showed her the original picture. Just as I'd hoped she thought that it was the same as the one published for all to see.

I let her stew for a minute or two before I revealed the truth and we burst into fits of laughter. That started a full on prank war between us. It became a game where we would try to catch each other naked and take pictures. I caught her getting dressed, she caught me in the shower after I forgot to lock the door. You get the idea.

I decided my best chance was to get her while she slept. I waited for her to go to bed, gave it another half hour to be sure, then crept into her room, my phone ready in my hand. What I saw stopped me in my tracks.

Sarah was laid out naked on the bed, legs up in the air and fucking herself with what I can only call a monster dildo. I mean this thing was huge. It wasn't just the length, although that was more than enough, but the girth of this thing. It was so big she needed both hands just to hold it.

I stood in the doorway for several seconds watching shocked. My mind was reeling with questions - How? Surely something that big had to hurt? And again, How? It didn't seem physically possible that it could even fit inside her relatively small frame!

Sarah moaned quietly, as if she was trying to keep silent but couldn't quite help herself, and it broke my reverie. I remembered why I was there and lifted my phone, pressing the camera button. There was a bright flash, Sarah screamed and dived for the bedsheet and I dissolved into howls of laughter "Got you!" I declared triumphantly.

Sarah didn't take it the way I expected. Instead of joining in with my laughter, she spoke in a quiet, timid voice, completely different to how she normally sounded "I need a minute, OK?" I stopped laughing, suddenly it didn't seem so funny. I nodded "OK" and backed out of her room, gently closing the door behind me.

It was more like 5 minutes before Sarah's door opened and she crept out wearing her robe. "So that was pretty embarrassing, right?" she said. I was so glad she wasn't going to try to sweep it under the carpet "Yep, sorry" We sat quietly for a few seconds, both trying to think what to say next, then trying to speak at the same time. I let her go first. "How much did you see?" she asked

"Not much with that tree trunk in the way!" I replied, trying to lighten the tone. Luckily she laughed "he is quite impressive isn't he?" "Impressive? He's - in fact wait there a second" I quickly jumped up and went to my bedroom, sorting through my toy collection. I came out holding my biggest dildo, 9 inches long and thick enough that I could barely wrap my hand around it. "This" I waved it in front of her "is impressive. What you had was something else entirely!"

Sarah got up, and I worried I'd upset her again, but she quickly returned carrying the monster. She held it next to my dildo for comparison. It was easily 3 inches longer, and at least twice as thick." You're right, when you look at it like this it is a bit big isn't it?" She giggled again.

We talked back and forth for a couple of minutes, mainly making stupid size related jokes, before I asked the question I really wanted an answer to "But how? How do make that all fit? I mean mine hurts so much I barely use it!" "I don't start with that one" she replied "I've got a smaller one about the size of yours that I warm up with first. Plus of course there's lube. Lots and lots of lube."

It was my turn to feel embarrassed. "I've never used lube, just what I... um make myself. Isn't that just for people who like doing it 'back there'?" "Oh you poor thing! No wonder it hurts!" Sarah responded "wait there, let me get some." She returned with what looked like a soap dispenser, complete with a pump nozzle at the top. She squirted some into my hand. It was a cold, clear gel. I thought it would feel slimy, but it didn't really feel like anything. It just made my fingers slippery. "rub that all over the top and shaft" she instructed me. Sarah squirted some more into my hand "then you put that on yourself, where it will do the most good." She ended with an exagerrated wink "What here and now?" I squealed. "I actually meant in your room, but now you mention it, you do owe me!" she was laughing as she said it, but there was a challenging look in her eyes. Well I've never been one to back down from a dare.

"OK then, I will!" I said. "Just one problem. How do I get these off" I pointed at my shorts "while I've got my hand full of this?" "No problem at all" Sarah said, leaning over to undo the button and hooking her fingers in my waistband. I lifted my hips from the settee and she quickly pulled my shorts down to my ankles and off. I probably don't need to tell you there was no underwear to remove. I kept eye contact with Sarah and slowly and deliberately smeared the lube over my pussy.

Sarah looked down as if inspecting my work, then nodded, smiled and said "Good. You'll also want to put some inside though" She squirted some more lube on my fingertips and as I hesitated said "Well? Go on then" I tried not to think about the fact that I was basically fingering myself with my housemate watching, but I won't pretend there wasn't something arousing about the whole experience.

My fingers inside me felt different. Not in a bad way. It was more like how I felt after a long session of foreplay and I was ready for the main event. "Now try with this" she said handing me my dildo. I figured that since I'd come this far already it was way too late to back out now.

I put the head against my entrance and gently pressed inwards. It. Felt. Incredible! I could feel myself stretching as the dildo filled me, pressing on my inner walls from all sides, but there was none of the pain I was expecting. I started to push it slowly in and out, my thoughts focused on how the sensation changed with each movement. "oh that feels sooo good" I muttered, closing my eyes.

"Here, try this" Sarah said, and I yelped as I felt something cold land right on my clit. "sorry, I guess I should have warmed it up first" she giggled. 'You think?" I replied as I got back into my rhythm, pulling the dildo nearly all the way out then pushing it deep inside me once more. I took her advice though and sent two fingers across my freshly lubed clit. I'll admit it did feel good and I started moaning softly with each slow thrust of my toy.

I could hear Sarah breathing hard and I opened my eyes to see her sat inches from me, her robe open and her hand lost between her thighs. "you're getting off on this!" I accused her. She just grinned and carried on with what she was doing. "well it is pretty hot watching you, you know." Hearing that threw me off a little and I pulled the dildo out a little further than I meant to. There was a soft wet 'pop' sound as it pulled free from my pussy. Before I could slide it back in, Sarah said "wait, try this" and passed me her monster, quickly covering it in a fresh handful of lube.

"Well she's been proven right so far" I thought to myself and took it from her. I still had my doubts, but I positioned the head against my entrance and pushed. I really tried. I did. I could feel myself spreading against the head, but it just wouldn't go any further. "Ahh let me" Sarah said. "Lay back and lift your legs up high" I thought back to the position I'd first caught her in and couldn't help laughing before copying the pose.

Sarah knelt in front of me, the monster dildo in both hands. She lined it up carefully and pushed. My world exploded. I couldn't feel anything except the toy inside me. It wasn't enough to say it filled me, this was far beyond that. I was stretched so wide I could feel the shaft moving against my clit with each thrust. I took control of it then, holding it with both hands as I'd seen Sarah do, driving it in and out, wanting more, wanting it deeper even though I knew it wasn't possible.

Over my moans, I heard Sarah making similar sounds. She was riding my dildo, bouncing up and down on it with her eyes glued to my pussy. Seeing my toy inside her, knowing it was still wet from being in me... That was the final straw. I came. Hard. I screamed something. It might have been her name. Whatever it was, it set Sarah off. I saw her push down hard on the dildo, grinding on it as she frantically rubbed her clit "oh fuck!" she screamed as the orgasm drove through her.

She collapsed down next to me, panting heavily, the two toys laying between us, both glistening with lube and our juices. Neither of us spoke. I don't think either of us could, but sometimes words aren't needed.