To insult or offend someone you are close to or are friendly with, unprovoked.
To drop a nuclear-insult on someone, with no prior warning, for no reason.
--often followed by immediately walking away after issuing the insult and ignoring any commentary or reply from the victim.
Dusty (walks into your office without knocking): You're pretty gay today. I'm sure your dad's proud, since he likes the dong, too. (turns on his heel and leaves)
Victim (stammering): ...wha...well...hey! Your dad like to...shit. Too late. He walked away.
Victim's Office Mate: Bro...you just got beached!