Expression used to mimic the diction and inflection of Cantonese. The long O and short A can be held for as long as the speaker sees fit. The intended effect is mainly for humor, invoking the image of a asian person vociferously expressing displeasure. Actual words presumably mean nothing.
Person 1: Hey sorry I'm late; were you waiting long?
Person 2: Do-Mah!
do·mah (DOH’mah) n. One who is unintelligent or not cool. A slur most often spoken by kids in the 8-12 age range.
“You told Mom about us using her maxipads as beds for our Barbies? You are such a DO-MAH.”