I'd say my two most overused words are "probably" and, sadly, "************".
The first one because I like to be leave room for error. I pretty much never use "definitely" when I could use "probably" instead.
The second one I use to refer to anyone who is not currently within earshot. Example:
"Damn, that ************ made some superb brownies."
Which sometimes catches people off guard because I try to pronounce it as eloquently as possible, saying "************" instead of "muthafucka".