person 1 "where you going mate?"
person 2 "i gotta go hang a dirt bird"
person 1 " i just had sex with a frog"
person 2 "oh your a f**cking dirt bird"
A Dirt Bird can also be someone who'll do anything to finish something, low morals. A person that'll stoop to anything, basically.
He's a Dirt Bird.
Yer ma's a Dirt Bird.
(simple exclamation from a crowd to a single target) Dirt Bird!