Infatuated with facts? Wikipedia has articles about Professor X and Axel F. Go learn something.
Professor X had ONE weakness is a YTMND created by Super-Penguin and created it on August 7, 2005.
The image provided in the YTMND is actually from an undisclosed edition of the X-Men comic book series. No one, the YTMND author included, has appeared to come forward with the specific episode this image was visible on.
The humor of the statement is that Professor X is all but invincible, but the fact that he is confined to a wheelchair makes him vulnerable to accidents involving staircases.
This specific YTMND has spawned sever "...One Weakness" fads which visualize the most common Achilles Heel of household names, places, and people.
Most commonly bashed is the Windows operating system for PCs as well as several video game and pop-culture icons.
The sound file accompanying this is a digital remix of the Alex F tune, first seen online in ABS'sRGB.