(noun) one who not-so-convincingly overstates their personal experiences, usually in contrast to another's. He or she believes their story to be convincing beyond all measure.
see also, "One Upper"
Me: "I used to love driving on the Autobahn when I was in Germany. I actually got my car up to 110 once. It scared the shit outta me."
PoserPro: "Yeah, I got my car up to 120 on the Thruway a few days ago and got a ticket. I need to go to court tomorrow."
Three days later...
Me: "So, how'd it go in court?"
Poser Pro (having forgotten his story): "Wha-??"