I’ve looked this up before. Multiple times. I can’t recall what I’ve learned before. I think if memory serves, which I’m not sure it does: the consensus is that it’s basically nonsense.
I mean, can we trust Hamlet’s translation that it means mischief? I think it’s more than that. What we can know for sure is that this is a hell of an alliterative sentence and that there’s bound to be some merriment in the making of all of those M sounds. It is Hamlet playing with sound, if nothing else. But it may well be something else. I just can’t remember what.
The Hamlet Project 