I think I'd have a challenge playing any character that was super verbose, spoke fast, used lots of words, long explanations, and so on. I don't know how I'd remember all of the lines, nor does speaking at length and really fast come naturally to me. Fast, energetic short, sure; long, nuanced, witty and such, not so much.
Basically, think the sort of character Vince Vaughn *always* plays - I wouldn't be able to do that. lol.