Agreed with the other poster that it's likely just a habit of substitution and other avoidant behavior. I used to be that way and it was a lot worse. Now I have a mild stutter and work as a corporate lawyer, giving presentations and talking on the phone all the time. No one gives a shit if you stutter as long as you adequately convey yourself. Being cute trying to substitute words and pass off blocks as something else only a) looks disingenuous b) wastes time and c) reduces clarity and precision. I found that the disfluency improved once I accepted that it was there