Homosexual, i.e. "used to be men but now are "ex" men".
Source: UK
xippie
n.
Pronounced "zippie". A young person who pretends to be a hippie. Created from combining "generation-x" and "hippie" - "My son and his friends are becoming xippies.".
Source: circa 1998, USA (SC)
xma
n.
Misspelled eczema.
See also: you'vegotxma
XmX
n.
Refers to a guy who is really hot n u want to get in his pants.
Source: circa 2003, USA
xyz
abbr.
eXamine Your Zip. Pretty much the same meaning as "Flying low".