My one is "shetai"
My cousin's: Paradox, where he uses it everytime he sees a contradiction.
I used to like Doc's old sig: "I can divide by zero."
Bet orphy's one (which can double as a pick up line): jhakkas maal
A memorable one from tv natok: jaan mia half pant poira ashen
Of course, there is the famous Joker's: "Why so serious?"
So what would be YOUR catchphrase?