"Fuck your mum", very offensive if misdirected at a Vietnamese speaker, and mildly offensive or even playful among familiars.
Origin: Vietnamese - common usage amongst Caucasians noted in the Springvale area.
"What the hell? Do ma!" - surprise, disdain
"Do ma fuck you!" - affectionate playful jibe
"Do ma mae" - this person seriously has nothing to say, and simply emitted this sequence of sounds out of habit.