It's funny because it's true.
When friend-of-a-friend-of-SFist Mike had a particularly nasty Muni experience, he struck back as best a person can: with a satiric t-shirt! He adds, "These ship in a couple of weeks. I’m sure MUNI will still suck by then." Zing!
It may not fix Muni, but at least you'll feel as though your shirt is issuing some comeuppance. Pick one up at the Feed Store -- sizes range from "Medium" all the way up to "Person Who Sits In A Chair All Day."