Mwa is a term that is generally accepted to mean a broad range of things. Most often said multiple times if it is mentioned, such as "mwa mwa mwa mwa mwa." Usually when there is nothing else to say, mwa is a suitable replacement.
Derek: Dude this quiz is going to be hard.
Sammy: Mwa mwa mwa mwa I know.
Derek: Mwa mwa mwa mwa mwa mwa.
Sammy: (as in reference to being Derek)Mwa mwa mwa I'm getting pit stains!
An acronym that stands for Man Whores Anonymous. Essentially a self-help group for those male members of society that find themselves unable to date single women.
Jason: I can'thelp chasing girls that have boyfriends. What should i do?
Christine: Jason, you need help. have you thought about attending an MWA meeting?
1. mwahahahahahaha
2. word used as punctuation of sorts, usually place at the start of a sentence.
3. somethingIRC junkies inevitably say at least once.