About T-Shirt Design
If you like shirts that actually have some personality, Irish O Meter T-Shirt is a good example. It fits really well with St. Patrick's Day, but you do not have to be obsessed with that stuff to enjoy the joke.
You could wear it for St. Patrick's Day, bring it out for parades, or just keep it in the normal shirt rotation. This funny t shirt is simple, easy to read, and does not need a huge setup for the joke to work. It has the same easy attitude people usually want from sarcasm shirts without sounding forced. The joke is quick, the message is clear, and that is really all it needs.