When a girl has sex with a guy because she feels sorry for him. This can be a boyfriend that she is no longer interested in or a guy who follows her around with sad puppy dog eyes.
Girl 1: I had sex with Dylan because I felt sorry for him. I hope he will go away and leave me alone, now.
Girl 2: What? You gave him a Sympathy Fuck? He is going to stalk you now!
After a long night of getting ham hocked and consequently defiling a friend's apartment, the accused purchases a box of sympathy donuts in lieu of a formal apology before sneaking out the back door.
KA was quick to purchase a dozen sympathy donuts in order to atone for his use of the ultimate shocker on She-Ka within the airplane bathroom of Navin's apartment the night before.