A Donny is not something you can define, it is just something you are after passing the Donny trials.
Anti Donny: I am a Donny.
Me: You are not a Donny. You have not passed the Donny Trials yet.
a strange fella to say the least. Not derogatory but slighlty insulting in an amusing way
person 1: Ayooo look at person 3, hes a strange donny haha
person 2: lmaoo yeah that dude is an odd one fr