Apparently he got pissed that people were walking in the stands during play.
He'll likely get suspended by the ATP for this.
Nick Kyrgios began his rant at an Italian Open spectator by shouting: "F***ing r****d bro."
Kyrgios then said: "You're not supposed to walk across the court as I'm serving, do you understand that?
"It’s b********, I don’t want to play when this s**t is going on."
As he packed his bags, Kyrgios said: "I’m giving 110 [per cent] and having to deal with f***ing idiots like him.
"I’m done, I’m f***ing done. F***ing done with it."