Quite Possibly the most useless internet/chat abbreviation known to man. 'nm' can be short for one of two things, 'Never mind' and 'Nothing much'.
Commonly misinterpreted by users, the abbreviation can be harmful, even fatal.
'Hey fag! You best not have spent all my money. What did you spend it on?'
'Well I do fucking mind you worthless shit! It’s my bling! Ima come around and cut your balls off and put them in your mouth!'
The previous was a common occurrence where Person B merely stated that he had not wasted much Person A's money, however, he got dead because he used the vague term, 'nm'.