Haxor is slang for hacker. As with all slang, hax0r can be used for many purposes.
1) Used as a term of appreciation
2) Humour, insult
3) To reveal the truth that you are a real newb
4) As a war call or to cheer another on.
1) Thanks for hax0ring that three hundred dollar aluminum case so that Zalman fan would fit. I'm glad you have such a handy bag of haxor tools. I know I don't have an eighteen inch set of metal cutters.
2) That newb is l33t h@x0r.
3) i r l33t h@x0r! All that neon light adds at least 15MHz to the system. Serious! Mitnick told me it does on IRC.
4) Haxor! Haxor! Haxor!