Australian term meaning a bad shag/f*ck. The word can be either used to describe the act itself or the person.
person 1: 'What happened last night round Brad's house then? Did you sleep over?'
person 2: 'Yeah'
person 1: 'Well, what happened?! was he any good?'
person 2: 'Not as great as i thought, he's/it was such a dud bash!'