This CafePress store sells t-shirts with offensive messages spelled out in "binary" (binary representations of ASCII characters, I'm guessing), including "Fuck Karl Rove," "Bomb, and "I am a Terrorist." Link
Update: Erik sez, "I'd get one with a truly random string of Characters on it. When asked what it says, I'd say "nothing, it's random ones and zeros." Which will mean, of course, I'll be thrown off the plane for having a shirt that says nothing meaningful whatsoever. What a lovely and useful precedent!"