Overexaggeration differs from mesoexaggeration (commonly known simply as "exaggeration") in that mesoexaggeration strays from the truth to balance out skepticism, while overexaggeration goes beyond this to a non-believable, completely ridiculous extreme.
Tim: Me and my brother Joe took out four guys at this UFC fight thing. I can bench press 225 pounds. I got a 25...wait a 26...wait a 27 on the ACT.
Me: Tim, let's have a chat about this thing called exaggeration. Or, in your case, overexaggeration.