Take the cake
Definition 1 of 2
Pro Tip 1/3Subjectivity
Can imply different things based on the speaker's tone and context; may be positive or negative. 
You forgot your anniversary again? You really take the cake!
Pro Tip 2/3Not Literal
It's a figurative phrase and doesn't involve an actual cake. 
His excuse for being late really took the cake.
Pro Tip 3/3Colloquial
Best used in informal conversations among friends or in casual settings. 
Of all her performances, this one takes the cake!