If you are at a party and all of your friends have hooked up with someone and it's just you and one of your friend's fuck friend's bros/girlfriends/what-ever-the-fuck-people-call-friends-nowadays.
Anyway, if it's down to just you and them and you friends need them out the way to have a good night, a sacrifice fuck is when you give up yourself for the good of your friends.
Donna: Betty, Megan and Emily had all hooked up.
Donna: Yea, but, I was all alone and the guys they were with had this loser friend with them who kept saying "bros b4 hoes", and "let's go man these hoes are prudes".
Kera: So whaddya do.
Donna: I sacrifice fucked him in a back alley so the girls could enjoy their boy toys for the nite.
Kera: You are a true friend.