My dad used to wear a "Beach Bum" t-shirt. Once after a contentious baseball game, a kid from an opposing team said to my dad, "You've probably never been to the beach!" Touché. When several of my friends used to wear obligatory early-90s Big Johnson t-shirts, I probably told them, "You've never even seen a big Johnson." Basically, if you're trying to be awesome because of your ironic t-shirt, you've got to be ready to whip out your swimsuit.
Just like the Big Johnson shirts, however, the All Balls shirts aren't meant to be literal. I'm sure a literal interpretation would be against dress code. It's also a silly visual because really old men with dimensia and sagging testicles represent a better literal interpretation of the moniker. But the meaning is the challenge of this message. This young man is saying he will do anything to demonstrate his coolness, and that's dangerous. Like, if you ask him to eat a stick of deodorant. Or bite the head off a small fish. Or jump down a flight of stairs. How can someone wearing such a bold message say that doing anything is just too stupid?
I can only hope that his friends have the sense not to ask him to cook a NyQuil chicken or stuff marshmallows, nutmeg, or whey protein in his mouth. I hope they don't ask him to swim across local ponds or file his teeth to look like a vampire. The problem is that they are dumb teenagers (we've all been there), so if they can get someone to ride a bike blindfolded while wearing a tutu, they will. Wouldn't you?
[UPDATE]
I was watching an episode of MST3K from the early 90s when the host made fun of the No Fear t-shirts as a thing, and then I remembered this original version of the All Balls No Brains shirt. I guess No Fear is more unisex, at least.