A nice bit of Irish Slang

this comes by way of christina, who's been boning up on her Gaelic slang as well.

Undy-grundy (n): wedgie

And here are some phrases I don't know how I managed without so far:

As rough as a bear's arse
As scarce as hen's teeth
As sick as a small hospital
As small as a mouse's diddy
As thick as two short planks
As useful as a lighthouse on a bog
As useful as a cigarette lighter on a motorbike.
As useless as a chocolate teapot
As useless as tits on a bull