I don't see anyone wearing shirt with flags on them. I do however see lots of people wearing shirts that list all the important places they've been.
NEW YORK
LONDON
PARIS
SYDNEY
ROME
In big white letters.
In my opinion this is only tolerable if you replace Sydney with a unimportant rural town or a really shit suburb.
Suitable places include:
Wagga Wagga
Parap ( I actually have a shirt with this on the list above)
Humpty Doo
Dubbo
Winton
Happy Valley
Tennant Creek