마빡
Forehead or face
E.g.  마빡에 기스나기 싫으면 주둥이 닫고있어.  Keep your friggin mouth shut or I'll stab you right on your face!

마짱뜨다
To fight

막가파
Someone who does things without considering the consequences, an impulsive + reckless person, someone who sows wild oats

만땅
To fill to the limit, to fill something full
E.g.  (At a petrol station) 만땅이요.  Fill her up, please.

말리다
To go pear shaped, to have a bad hair day

망가지다
To embarrass oneself

맥주병
Someone who just 'sinks' like beer bottles when put in water.
E.g. 나 맥주병이야.  I can't swim at all.

먹다
To have sex with someone
E.g. 내가 니 깔 먹었어.  I fucked your girlfriend.

멍텅구리
A retard

멍청이
A dickhead

면상
A derogatory term for face

몸빼바지
a kind of trousers that used to be 아줌마's favorite fashion item like a couple of decades ago.

몽땅
completely

물먹이다
To stand someone up or to disappoint someone intentionally, to pull someone's leg

무지무지
an intensifier meaning very very
E.g.  무지무지 커.  That's humongous.

무지하게
also pronounced [무쟈게]
an intensifier meaning very