What's a short, clean joke that gets a laugh every time?

EDIT 1: Clean = no racism, sexism, religion-ism (if there's a word for it), etc.
EDIT 2: I'll never understand Reddit's love for penis jokes. I've seen at least 20.
EDIT 3: Holy shit, you guys.
EDIT 4: I'll never understand Reddit's love for penises in general.
EDIT 5: WOO GOLD!!!! And the amount of times I've seen the "brown and sticky" joke it TOO DAMN HIGH!
EDIT 6: GOLD AGAIN!!! It was a good day

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