when someone types you "lmao k" they are in most cases really mad or they don't believe you
lmao means "Laughing My Ass Off" and is mostly used in positive way but when combined with "k" then the meaning is turning negative.

A man who messes around with other men, but no one would ever know by looking or talking to him. Used by gay black men to identify masculine gay men or DL Brothas.