I have been getting a lot of crap about spelling moustache the way i do. Well here is some information via the keeper of the laguage, the Oxford English Dictionary.
In old moustache (see sense 5) after French vieille moustache, lit. ‘old moustache’ (1817 or earlier; cf. moustache soldier (1745)).
With sense 4 and moustache monkey (see sense Compounds), cf. MOUSTAC n., moustached monkey n. at MOUSTACHED adj. Special uses.
In present British use the unaltered French spelling moustache is almost universal, but the earlier British dictionaries (Johnson, Walker, Smart) and most American dictionaries prefer the semi-Anglicized form mustache, which predominates in American usage; exceptionally the third edition of Webster (1961) gives moustache as the principal headword spelling, but later editions of Webster’s New Collegiate Dict. (from the 8th ed., 1973) give mustache. With regard to the pronunciation, N.E.D. (1908) s.v. states that British usage was divided between (u) //; and () //; in the first syllable; and that in the United States () // appeared to be general. In 19th-cent. sources the quantity of the vowel in the second syllable varies, but stress is regularly marked as falling on the second syllable.]