Strange choice of words

[frozen-jelly.livejournal.com]

While reading Sirius' latest entry, I noticed this sentence:
"Nothing's worse for a flu than getting up one's Irish (and, er, Molly's got more than most, old man)."

I have absolutely no idea what this is meant to mean. I can only guess it is some vaguely racist use of the word Irish to mean angry or frustrated, which is very odd. Can anyone shed light on this usage, I have never heard it before? It really makes very little grammatical sense.

Comments

Re: OED

[lapin-agile.livejournal.com]

The OED's identification of the phrase as a US usage surprised me, too, though I couldn't have told you where or whether I'd actually heard it before. And I don't know what to make of the OED's specification that it was originally US or that it is/was "dial" (dialectal, I assume, but which dialects?).