A derivative of the traditional "moot", which is originally a noun referring to a hypothetical legal case (as practiced by students). Then used as an adjective as in "a moot point", meaning "a point open to debate".
As of the mid-1800s, "moot" has been used to refer only to the hypothetical aspect of something termed "moot", i.e. that something is "of no significance" or "of no relevance".
"m00t" is an exclamation meaning "I have made <subject> moot."
I flamed him. He is toast. m00t.