Language is very cool and funny to think about. I tend to pick up expressions from people fairly easily, then I have to wonder - how did that happen?? It's been going on my whole life, though...I am a sponge...assimilate or die...etc.
When I was hanging out in Harvard Square, it was hip-hop speak like
"Word" to emphasize a point.
An old boyfriend got me in the habit of
"Back in the day"...at least I didn't pick up
"old school" from him.
Worse than genital warts, I swear!
And of course
"I swear" and
"Tell you what", though I could argue that those shouldn't count.
Lately it's Buffy-speak like
"<adjective>, much?" and making adverbs out of any words that come to mind.
My #1 peeve expression, though, is
"rule of thumb." This phrase never fails to annoy me since I first learned its history - evidently it refers to the diameter of the rod a man was allowed to use to beat his wife during Colonial days.