The other day I saw about 15 Americans together walking up Regent St in London all wearing sweatshirts with 'USA' written across them massive letters covering their entire, rather generous, torsos. That was overkill. I cant believe at least one of them didnt think it a bad idea.
It probably had to do with the Olympics. There's no way 15 people would agree to dress exactly the same, and especially in shirts like that, unless there was a reason. If it wasn't for the Olympics then definitely they belonged to a club.
It wasnt a sports team unless eating has become an Olympic event.
Are you sure all 15 looked like that? I find that so odd.