Madonna -- Drops N-Bomb on Her Own Son

Madonna has a strange way of bragging about her son -- she posted a pic of him boxing with the hashtag ... "disni**a" ... and she immediately got blasted for it.

Madonna posted the photo of Rocco Ritchie on Instagram Friday night with the caption, "No one messes with Dirty Soap! Mama said knock you out! #disni**a."

Dirty Soap is clearly a nickname for Rocco. As for the hashtag -- who the Hell knows?

Some outraged followers ripped her for it ... with comments like, "MADONNA U NEED TO TAKE UR arthritis medicine instead of trying to be hip on the internet."

#truth.