One of my "old college buddies" (yeah, all right, I only graduated like 6 years ago) use to mimic this for me all the time. I would fall over laughing every time but had never seen it for myself until today. Someone in my office said "old man," to which I spouted this impression of an impression...of an impression. I then had to explain, which led me to look for it on the magical interwebs (seriously, what the hell did we do without it?!).
Anyway, enjoy, it's awesome (the first bit is the one my friend would crack me up with):