The Pants Alternative - S3-E18
Corrected entry: Sheldon claims the X-Men were named so after the X in Charles Xavier's' name. In The X-Men #1 (1963), Professor X states that mutants possess an extra power that humans do not have. Xavier then says "That is why I call my students... X-Men, for EX-tra power!"
Correction: He may be going by the movie continuity, where the X-Men DID name themselves after Charles. (Likely in an effort to "dumb it down" for Penny).
Captain Defenestrator
It could also have been deliberate on the part of the writers as a set-up for Sheldon's "C-Men" punchline.
Cubs Fan ★