A misspelling of 'monkey', that came from the word spnak.
Back on Usenet, if you wanted to kill a stupid thread, you'd quote the relevant part and then say
SPANK
in order to stop the thread in its traces. Someone (perhaps B1FF? See also JeffK?) one day said 'SPNAK', and the rest is history. DanielLawson likes that word for some reason.
SPNAK style mispellings have been a trait of Junyer who probably passed it on to everyone else ;)
We use 'mnokey' interchangibly with 'stupid person'.
Needless to say if you spnak the mnokey too much, you'll go bilnd.
See:
2 pages link to Mnokeys: