My father plays in an amateur band and invited me and my girlfriend to a festival. We were to sleep in a large tent with all his band members. After they'd had their concert, the drinking got out of hand for all parties. My girlfriend and I made a dumb bet with our father. If he won, he would get to sleep with her. If we won, we stood to win a rather large sum of money. We thought it was all in good fun and honestly, the money was tempting.
And then we ended up losing that bet. My father wouldn't let us off the hook. He insisted we go back to the tent so he could collect his prize, that is to say, my girlfriend. There were several problems with this. We'd never done it before and my girlfriend was a virgin. He told us he would take her virginity and this would help bring us closer in our relationship. I didn't feel like watching, but neither could I just abandon her. At this point we really regretted it all.
So, he got her lower parts undressed and got on top of her on a sleeping mat. While I held her hand, he put his penis inside of her. It really hurt her and he looked like he was about to get a heart attack, moaning and breathing heavily. Adjusting took both parties quite some time. My girlfriend not hurting so much and constantly going "Ow" and "Oww." And my father not having some sort of medical event.
Finally, things had calmed down, and my girlfriend let go of my hand to put her arms around his shoulders. The intercourse he performed with her was in a slow and steady tempo. I didn't know what to do with myself, so I just sat there watching. He of course came with some lewd comments, like "I just took your girlfriend's virginity" and telling us how he was going to make her pussy smell like fish. At one point he told us to kiss each other, which we did. While she embraced me his movements got harder and more authoritative, just to make a point, I guess.
There were people coming and going in the tent, and eventually all the other band members had returned. They of course realized what was going on, and knew the relationship between us, but were kind enough to not make any comments. For me it adds to the humiliation that my father's friends know exactly what he did and that he was sleeping with my girlfriend right in front of me.