I was staying with my girlfriend while her parents were away on holiday so she would feel safer and have some company while they were gone, both of us early 20s at the time. One day, she needed to go out and grab some things, return some clothes she wasn't feeling too good about etc, and I decided I didn't feel like going out so would stay in instead. Of course, being early 20s and having the house to myself, I was getting pretty horny. I would normally wank at any given opportunity whenever I was home alone so it felt right to get started on myself.

Now, a bit of history about this, her mum knew what my cock was like after two incidents. One, they were drinking together one night, got a little drunk and my gf told her what my cock was like. And another time, she walked in while my gf was sucking my cock and I'm 99% sure she saw for herself. Knowing this and with it firmly in my mind being in their home and all, my horny brain thought it was a good idea to grab a pair of her panties from the laundry pile and have a play around with them.

Stupidly, I'm in the living room, boxers round my ankles, stroking my cock with some porn on the laptop. Wrapping the panties round myself and rubbing up and down to some milf porn. I get about 10 minutes into this before I hear the door open and my gf is back cos she forgot something. Sees me and my fumbling trying to do something, anything, to hide what I'm up to to no avail. It's obvious what I'm doing and what I'm using. Mortified, I expect some trouble from this.

Quite the opposite as it turns out. She calls me a dirty boy and then tells me to sit back down and she strokes my cock until I cum. No need for the panties. Helps she was a cock hungry slut of course, any sight of being naked and she's horny herself. Never did use panties to wank again after that, but fond memories of the one time I did.