Q: Why do Americans fish with guns?
A: To shoot up the whole school.
Alright listen up buttercup. This joke is dark. Like, "I haven't seen the sun in years" dark. It's saying Americans are using guns to "fish" as a euphemism for shooting up schools, which is a big problem over there. It ain't funny, but some folks use dark humor to cope with messed up situations. You wouldn't get it.