When: current day
Where: UK (and Ireland, if useful)
Previous research: minimal. I have no idea about the magic search term(s), ad I'm not even sure this is information people would collect/discuss.
1) It's completely unremarkable to see Americans wearing t-shirts with a "message" - a souvenir of some experience, supporting a cause, or even a plain corporate logo. Is this also true in the UK? (I think it is, but want to make sure.)
2) If so ... I'm looking for UK-centric "messages" that are provocative or cheeky without actually being offensive. (Unless, of course, one's /looking/ for an excuse to take offense.) The wearer is in his mid thirties, a bit of a modern renaissance man, with the "traditional" English dry sense of humor. Pointers to images would be wonderful.
May 17: thanks to all who helped. I don't have a clear winner, but do have some ideas ad places to look into.