Off the top of my head, I'd go the DX non-crossing crotch chop (ah, the memories of being thrown in grade-school detention for doing such an edgy maneuver), Rocky's JUST! BRING IT! hand motion (also handy in instantly filling your Spirit Meter in "No Mercy"), and the Orton Pose, which also doubles as a good macro when you want to boast about your team's 5-2 record in the Fantasy Football League of DOOM! \_O___/
Bonus question: Dumbest taunt ever? Easy candidate for me, although you may not remember it: Orlando Jordan drawing a big "O" and a big "J" in the air with his finger. That alone deserved the 25-second tapout at Summerslam.
- Benoit / AA's "cut the throat" gesture.
- The Orton Pose, because he's a living video game character anyway.
- Randy Savage's twirl-and-point, and/or the pre-elbow pose.
And yeah, I can't imagine any worse than the "OJ" one.