do (one's) damnedest

To put forth the maximum amount of energy or effort toward some task or goal. Money is a little tight at the moment, but I'll do my damnedest to be there for your wedding. I'm doing my damnedest to get a passing grade in this class.

do your damnedest

INFORMAL, RUDE

If you do your damnedest to achieve something, you try as hard as you can to do it. I did my damnedest to persuade her. She was doing her damnedest to look as if she didn't care. Note: People sometimes use try instead of do. Ted tried his damnedest to explain things.

do (or try) your damnedest

do or try your utmost to do something.

The superlative form of the adjective damned is used here as a noun and can mean either ‘your worst’ or (more usually now) ‘your best’, depending on the context.

do/try your ˈdamnedest

(informal) try very hard; make a very great effort: He was doing his damnedest to make me feel uncomfortable so that I would leave.