setting the scene;
Your drunk on a night out, you meet a girl, you go back to hers/yours and have drunk sex.
Now it's the morning, you wake up with an almightly hangover and whoever you've pulled.
No-matter if shes the hottest girl you've ever seen or the worse you've ever seen you will still have (or at least try to have) sex...because you have 'the hangover hots'
friend 1: yeah i took her back to mine and we had sex, then again in the mornin
friend 2: was she hot?
friend 1: not really
Friend 2: well why did you go again in the morning then?
Friend 1: Had the old Hangover Hots
Friend 2: Textbook