I’d wear them to class sometimes when I was in college. I wore them to a Super Bowl party at college. Otherwise, only at home.
I don’t even own a pair of sweatpants. But since the companion thread to this one is “The least formal place you’re worn fancy clothes”, I think it’s within the spirit of this thread to post the most formal place I’ve worn casual clothes, even if they weren’t actually sweatpants.
About 10 years ago I went to a play at the Sydney Opera House in shorts and a tshirt. Going to the play was kind of a spur of the moment decision. I thought since I was there, I should actually see a see a show of some sort at the Opera House, not just take a few pictures of it like most tourists. Except I didn’t actually have any fancy clothes with me. Apart from a few days in Sydney and a few days in Melbourne, most of my time in Australia was going to be spent out away from the big cities, camping and staying in hostels, so I didn’t expect to need any fancy clothes. But I figured Australia’s attitudes towards attire are a lot like California’s, right? Things are more casual there. But for seeing a show at the Opera House everyone else still wore way fancier clothes than me.
I was in Sydney looking for things to do. I saw fellow Canadian Michael Buble was performing at the Opera House. I’m pretty neutral about him - nice voice, dated songs, not particularly innovative - but I like some types of jazz and thought I’d see him perform, if only to be patriotic. There wasn’t anything better to do that night. I’m pretty sure I only had casual clothes and wore them.
I’m also pretty sure that I was one of the few males in the audience. Was it wrong not to suspect the vast majority of his fans were women, or was this an Aussie quirk? Dunno.