What the hell is up with the fact that the other person has to confirm it? Would it not be really awkward for girls you've hooked up with to know that you just marked them as "I hooked up with you" in your friends list, and probably worsen chances of future hookups with them? And I'm pretty sure that a booty call list is what they have in mind, seeing as how you can filter out your "hookup" friends on your friends page.