I've got a "Shrodinger's cat is dead" (with "not dead" on the back) shirt which helps me find interesting people (THE most random people understand it). I'd argue that's more useful than fashion (does it have a use?), and remember that stick-figure shirts occasionally explode in popularity (I remember a big burst several years ago). XKCD is just a superior-taste subset of those.

edit: heck, "fashion" hasn't served me too well anyway. I wore a blue-screen-of-death shirt to one of my interviews, and got the job. The interviewer called the boss in to laugh at the shirt :)