People wear literally anything.... some flats at uni we saw guys and girls walk round completely naked.... but its quite rare and never the attractive girls
Normally people just grab whatever, if we wheren't going out we'd lounge round in sweatpants, pj bottoms, vests, topless (i'm a guy lol) etc....
Reminds me of this guy in my halls actually, I'm quite average looking, not really that build but not really underweight and this really tall lanky guy always used to comment on how un-hairy I was and skinny everytime I used to walk about topless... Weird thing is I'm very adverage in all respects and without being cocky I do fairly well for myself :P
Anyway the amount of looks he got was hilarious seeing he was about 6'5 hairy like a bear and looked like a skeleton, lets just say the amount of times he got shot down by other flatmates was quite funny when he used to say things like that to me.
Anyway moral of the story is, as long as the clothes are fairly clean and don't look ridiculous people don't really care, any nasty people who do normally get a telling off.