banjax
A mess or undesirable situation made as a result of incompetence.
informal
I'm tellin' you the scholar, Bentham, made a banjax o' th' Will.
Where it comes from
Unknown, perhaps originally Dublin slang. According to Green’s Dictionary of Slang, may be a euphemism for bollocks.
Adapted from the Wiktionary entry banjax (CC BY-SA 4.0).