I understand why this is wrong (order of operations dictates the division happens first, so it's really 25 - 1 = 24), but why is it funny? I don't mean "This isn't funny," I think I'm just missing the joke.

4! Is meant to be 4 factorial. 4! = 24.

The fuck is a “factorial”? They didn’t teach me that one in high school math.

Im sorry your highschool curriculum failed to teach you. I learned factorals in jr highschool