There's a wide latitude in interpreting a theme-- hence killin' it with that throwback William Tecumseh Sherman frock coat at your cousin's '60s party! Enjoying similar variety, Shirt Fight
The pet project of a Chi couple with a fondness for tees and a robust network of artist friends, SF generates its shirts based on weekly battles in which a cavalcade of submitted designs playing on the week's designated theme vie for user votes until all but one are eliminated, like the Highlander but more ringspun-y.
The themes range from the most straightforward ("black and blue", which mandated designers use either a black or blue shirt and spawned "Party Machines" featuring a Bender from Futurama-esque bot rigging an oil bong) to more conceptual: the "emotions" contest winner was a frightening green fishfaced super villain titled "Angry Fishman Will Eat Your Face" -- but who could blame him for his angry face-eating, when deep down he knows his would be so delicious in a miso-soy glaze.
Other previous victors included "Death of a Sailor", an old diving helm done up in the style of a vintage nautical tat, or the winner of the age old "Robots, Ninjas, or Pirates?" debate, a watercolor-style crusty pirate captain titled "Old Sea Bastard", (Baby, I Got Your Doubloons, Don't You Worry).
The next winner to reach dizzying glory will have to emerge victorious from this week's "Faces" contest, for which you could have conceivably submitted your own messed up grill, but no one wants a reminder of your parents own Imperfect Union.