1) An emoticon, with ones eyes crossed and tongue sticking out. Obviously this means "retarded."
2) The most recent edition of the Windows OS, recognizable by the GUI that looks like it was made by Playskool, and the code that was probably written by same. The OS was named for said emoticon.
3) Short for Experience in many RPGS. Variant of EXP.
"Delete XP and install Slackware, dipshit."
"You need 100 XP for a level."