How do you define funny? What are funny t shirts?
Funny has a lot of meanings.
It basically means providing fun. But this can be subjective. Something that can be funny to one is not funny to another.
It can mean peculiar or odd. This is when political correctness is not a necessity. This isn’t the goodie-goodie funny. This is hard core funny.
As to funny shirts, do not be shocked if they offend you. They can be funny to some.