Can't decide which phrase is more deserving of death by firing squad......

[Hakluyt]

"Grow a pair" - particularly when referring to a woman.
"Cat's bum mouth" - used to be specific and funny- now means "She disagreed with me"- and usually-"She is older than me, therefore has no right to disagree with me"

YANBU to find them both incredibly annoying.

Was that the question?

Personally I think 'cat's bum mouth' wins.

Grow a pair is equalled in my book by "man up"

"Grow a pair" definitely wins: it's got all those echoes of totally false testosterone-laden concepts of masculinity and bravery. Even the most abject cowardly man has a pair of balls, ffs. And, as you say, it's utterly absurd when addressed to a woman.

I like "woman up" Greythorne. It works very well.

i like to hoik my big-girl panties