Mr. X is the male version of the letter "X" in the English alphabet. Mrs. or Ms. X is the female version. Since they have no genitalia it is hard to differentiate between the two.
by Junkrocka May 15, 2008
mister X is a person that you talk about with friends in code, usually a dealer of things that are code-worthy. See Mr. Nice Guy.
by mogrove42 July 21, 2006
Mr x is a person who is a threat to the one direction fandom they leave really strange messages and death threats towards the boys. They have been inactive since around 2013 but we still should look out for them.
by onedirection._obsession July 10, 2021