at wit's end

at (one's) wits' end

In a state of distress because one has no more patience or mental stamina, often after having dealt with some kind of problem or difficult situation. The baby's been crying for hours, and I'm at my wits' end! I'm already at my wits' end, so if this train gets delayed too, I'm going to scream.
See also: end
Farlex Dictionary of Idioms.

at one's wit's end

Fig. at the limits of one's mental resources. I'm at my wit's end with this problem. I cannot figure it out. Tom could do no more. He was at his wit's end.
See also: end
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • at (one's) wits' end
  • at one's wit's end
  • at wits' end
  • at your wits' end
  • be at (one's) wits' end
  • be at your wits' end
  • the patience of a saint
  • the patience of a saint/of Job
  • wit's end
  • up the wall
References in periodicals archive
At wit's end Crystal Palace v Spurs Crystal Palace manager Ian Holloway has had enough of being the class clown and wants to be taken seriously on his return to the Premier League.
At wit's end
But some critics find it less than shipshape, with Time magazine's Richard Schickel suggesting it be renamed "Pirates of the Caribbean: At Wit's End".
Pirates 3 plunders pounds 63.2m