last nail in the coffin

another nail in someone's coffin

An event that increases the likelihood of or causes further failure.

breathe one's last

To die.

cobbler, keep to your last

One should not criticise matters outside one's field of expertise; one should mind one's business.

dead last

Finishing in last place in a competition or ranking, often by a considerable margin to the next to last place finisher or after an exceptionally poor showing or season.

draw one's last breath

To die.

every last

every; without exception (used for emphasis).

fall at the last hurdle

To fail near the end of an activity, a project, etc.

final nail in the coffin

Something that is ultimately responsible for a previously prospective demise or failure.