My mom frequently says "whatever blows your skirt up," a colorful addition to the likes of "whatever floats your boat/trips your trigger," etc. Has anyone else ever heard this one?

Yes! Many are the times I’ve used myself albeit slightly altered: "whatever blows your dress up."

It’s especially jarring when said to men, and I particularly like the fact that it doesn’t rhyme.

inanna

Here’s one I used to hear quite a bit, but havent for quite a while "whatever grinds your cookies".

Bob

I heard this first as "...skids your wheels."  I suppose I think of these as similar to "One man’s ceiling is another man’s floor." etc.