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1.
Someone who jokes around a lot. Someone who tends to act a fool, yet in a humorous way. Everyone loves them a good ol' Duffa!

And there is also "Duffery", which is the proper word to describe the actions a Duffa takes!!
Sam: so, I bit my cat the other day.

Ryan: you silly Duffa.

Sam: I was just bored, bro.

Ryan: what's with all this duffery?!
by Cay Breezyy's January 15, 2012
 
2.
A more derogatory term of the word, doofus.

One who is stupid beyond all belief.
It was Jordan's 21st the other day and she was being such a duffas.
by Tim O'Houlahan November 27, 2010
 
3.
A boy who hits puberty way to young, and resembles a grown man by the seventh grade, who wears a taped pair of glasses and trips on him self often.
Hey you see that duffas over there trying to pick up on that chick, I bet he'll lose his balence in five seconds, lol!
by joe May 18, 2004