together. When something is haxtreme, it is above and beyond the normal hax or xtreme levels of awesomeness to describe something that has happened.
Captain: Wait, what? Did he...Did he just do that???
Corporal: He did sir! That is Haxtreme!
Combining the two words of hax
to form haxtreme. When something is haxtreme it is to be shocked or amazed and/or dumbfounded at whatever it was that just happened.
Can be used in gaming, txting or plain conversation if you're daring enough to not care what the other person might think of you when saying a ridiculous internet term/word out loud in RL.
Rose: "Wait, what? Did he just do what I think he did?"
Janet: "OMG yeah he did! Haxtreme!1!!!"