The act of having sex with someone that you have had sex with previously. A "bangover" usually occurs when you are intoxicated or just lonely. You typically realize why you stopped banging someone in the first place after your "bangover" is done.
Last night I had a few glasses of wine, was feeling kind of lonely, so I decided to have a bangover with Alex. This morning I remembered why I stopped banging him in the first place....no matter how hard he tries, it is just never going to get any bigger.