I wear shirts with old logos that are faded for real from the shirt being somewhat old (actually just one, a Mountain Dew shirt my dad gave me, and I don't wear it often).
Most of my other shirts are from conventions or are related to music, video games, or school (that is, they're purple and gold and/or they have a panther on there somewhere). Some of these categories overlap.
I have a couple of shirts that have "humorous" phrases on them (not the insulting kind), but they usually just sit in my wardrobe with the Mountain Dew shirt and the button-down shirts that won't really be fitting to wear until spring, when there's a good chance of them being too small. I agree that shirts that insult the reader or give the wearer undeserved praise are stupid. Also shirts with innuendos.
EDIT: My two gripes there also apply to sigs, mostly on other forums where, in tandem with emoticons and banner sigs and other junk, they make me want to tear my eyes out.