couldn't happen to a nicer

accident waiting to happen

A thing or situation which is almost certain to eventually lead to an accident.

couldn't be more different

Two entities that have virtually nothing in common.

couldn't care less

To not care at all; to have no interest or concern; to be apathetic.

couldn't carry a note in a bucket

Not musically talented, unable to sing.

couldn't organise a piss-up in a brewery

Is unable even to organise a project that requires no planning; is incompetent; used to describe someone as greatly incompetent.

couldn't stop a pig in a passage

To be bow-legged.

happen along

To arrive by chance; to occur by happenstance.

make happen

To realize, to cause or bring about a thing.