I think the most pervasive useless PA-ism has got to be visibility. I hear it all the time from guys who give an otherwise concise, informative PA. "Weather at the destination, calm winds, clear skies, good visibility, a temperature of XX degrees..."
I get that we're just reading it right off the ATIS, but do you think the average passenger gives two craps about the visibility? Unless it's a CATII down to minimums it probably won't affect their drive home. I feel like if you're going to give them the visibility you might as well tell them the altimeter setting because they probably care about as much. Most captains I've mentioned it to just laugh and agree that they have no idea why they say it.
"At this time" is the other one that drives me nuts. The airport is the only place you'll hear it and you can seriously hear it 9 times before the door closes. Have you ever sat down at home and said, "Alright kids, at this time we're going to eat dinner." "At this time, I'd like to ask that you take out the trash."