Gafgot
If you're a gafgot, you're either an idiot who can't tell a joke from a punchline or you look like an idiot who can't tell a joke from a punchline.
My friend said I looked like a gafgot when I tried to tell a joke but forgot the punchline.
At the party, the guy who spilled his drink looked like a gafgot. I told him he was a gafgot for spilling his drink.
My brother said I was a gafgot because I forgot the punchline of my own joke. I told him he was a gafgot for being an idiot.