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?!