When the guys mock my accent at the office, they sound like they are out of Goodfellas, or something. It's not that strong, but it's either go with a strong NY accent, or they go with a strong southern accent! Generally, they are all pretty awful!
I wouldn't think to mock the accents at the office, simply because I can't do a good one, and if you can't do it right, why do it at all?
I think Gary Oldman drops the accent pretty well. I mean, True Romance? I barely had any idea that was Gary Oldman to begin with!