Cantonese Joke

You won't get it at first if you don't know basic cantonese.

GATHER MY CANTONESE BROTHERIN~

But anyways, here's a breakdown of the punchline:
sup = 濕 = wet
foo = 褲 = pants

GET IT? /SHOT

Joke was made up by my friend at schooool. 8D
Sorry if my writing is too hard to read, ffff.