This was actually a little time ago. I was with my that time girlfriend in a sauna on pretty busy day. We both always loved to tease each other in public and sometimes we also went further but never actually with audience. So we were in sauna already horny from teasing each other and I had a tough time to hide my boner.

So we went into jacuzzi where already three other people already were in. She soon began to tease again, touching me and and so on. Her hand wandered down to my crotch where she felt my rock hard dick. She almost immediately began to jerk me off. The other people couldn't see it through the bubbles, but I had a hard time to pretend that I was just enjoying the relaxing bubbles. But I couldn't get her along with it unpunished. So I pretended to lay my arm around her but in fact reached down behind her back. She immediately lifted her ass so my hand could reach under her butt to her pussy. I began to finger her and we were getting of each other. All that while three other people were in the jacuzzi. We had a really hard time to behave like nothing would happen, so we could jerking and fingering really slow to not get caught. But it was unbelievably hot so we both didn't need much. I came like in 5 minutes from her stroking and shot my load in the tub. After that we both stayed for like 5 minutes more and left without the people noticing we were handjobbing each other.