About T-Shirt Design
What doesn't kill you makes you stronger Except for bears T-Shirt works because it sounds more like something a real person would say than a random slogan. Anyone who is into everyday humor will probably understand the idea right away.
It works for birthdays and casual days, but it is also the kind of shirt someone could wear whenever they feel like it. For a funny t shirt, it keeps things pretty straightforward and lets the saying carry the humor. It is not trying to be deep. It is just a funny shirt with a good line on it.