Here's my take on it:
He says "Pig". But you
could hear "shitbag" if you are sorta looking for it.
I put in the DVD and played the scene several times. He says "You stinking Irish pig". The "sh" at the end of "Irish" is drawn out and slurred, and then he drops to a whisper, then almost mumbles the word "pig". I suppose, since he didn't quite enunciate and draws the two words together, it could sound enough like "shitbag" to have someone get the IMDB quote listed.
Probably someone who has it in for the Irish!

(just kidding)
I called my wife into the room to give her 2¢ worth. I didn't fill her in; just asked what the guy was saying. She thought he said "prick". When I asked her to check a few more times, she stood by her thought. I then filled her in, and she went against me, saying it was "pig", not "shitbag" (I was leaning that way at the time).
Then she suggested we turn the subtitles on. It said "pig" in the subtitles.
Then we found my old VHS copy and played it. It was just as unclearly spoken on that copy.
Then we turned on the Close Captioning for the VHS. It said "pig" there, too.
I went back and replayed, closely looking at his mouth. I had to agree he said "pig", and never anything else...he just slurred the dialogue while saying "Irish" and "pig".
The IMDB is wrong, in my opinion.