a misspelling of funny then turned into a word used in place for funny devolped in the time of egyptians near the death of tutankhamun hence why funny rhymes with mummy
A "Dunny" is someone who scores 16pts on the basketball court despite possessing the most unco shooting action. This is coupled with the fact that he runs like a Welshman (retard).
That guy just pulled a "Dunny", he almosttripped over his own feet while taking that shot yet scored.
peter: "hey Jamal, can you pass the salt?"
Jamal: "i don't know peter, cAAAAAAAAAAAANNN I PASS THE SALT" *giggles*
Peter: jamal, you fucking dumbass, you're so dunny