As it goes, the "Don't yadda yadda the Lord" and "Fuck subtle" (although I can't wear that to work) T-shirts get my vote so far, but here's a new one, since I'm re-reading TC for the nth time:
Sleeve: Official DF logo (does one exist?) printed small
Front: Burning building (or something else messy, use your imagination)
Back: Wizard Peabody picture (severe look over spectacles and all) saying (yes, I want a caption bubble), "You are an untidy person." Then underneath that in block letters: "I get vicious under pressure."