Presuming that a girl in sweatpants thinks the same thing I do when I'm wearing sweatpants, it's hot because you see a girl wearing those and she looks normal. She's not made up to high holy hell trying to get the highest bidder, she's not wearing a meticulously selected outfit that she thinks will look better than the other girls that spent an equally excessive amount of time on their outfits, she's not trying for anything. She simply doesn't give a fuck. She knows you're into her and she just wants to plop on the couch, order a pizza, and watch a cheesy movie on HBO with you.

We appreciate the effort you put into your appearance ladies, really we do. But when you let your appearances down like that every once and again, there's nothing more attractive (unless you're in that mode and you give the little lip-bite "lets go to the bedroom" face, that's way more attractive).