I thought it was Ecstasy Mother Fuckers too.
But after seeing you ask this in the One Hit wonders thread, I needed to go research it.
Found out it officially stood for "Epsom Mad Funkers" when they started out.
The "Ecstasy Mother Fuckers" came from a B-side track of theirs called "EMF" where they mention the phrase.
But officially, it stood for "Epsom Mad Funkers"