#13 - Greg Valentine: I Broke Wahoo's Leg
HONORABLE MENTION: Ox Baker's shirts (they'd be on here for the same reason)
During an NWA Mid-Atlantic Heavyweight Championship match between Greg "The Hammer" Valentine and Wahoo McDaniel in 1977, the heel Valentine twisted Wahoo's leg to the point where it broke. It is likely that this was only in kayfabe, though it is possible that he actually did break his opponent's leg.
Nevertheless, the narrative was that Greg Valentine broke Wahoo McDaniel's leg to become Heavyweight Champion.
As such, the new champion would walk to the ring wearing a plain black shirt that read "I Broke Wahoo's Leg" on the front and "No More Wahoo" on the back. The shirt drew nuclear heat from crowds, as Wahoo McDaniel was a beloved babyface. Still, Valentine wore the shirt for months and months, helping to build up hype for Wahoo's eventual return.
Though it's one of the most memorable shirts in the history of professional wrestling, it places lower on this list because it was never officially released for retail sale at the time. So, many fans create their own versions of it and wear them to wrestling conventions. Additionally, it has inspired a few more recent shirts, such as CM Punk's "I Broke Big Show's Hand" shirt from 2010.