Kawhi Leonard's mother reached her boiling point at the Spurs game Thursday night -- going off on a heckler ... calling him an "a**hole" and telling him to "shut up."
It all went down in San Antonio -- where her NBA superstar son returned for the first time with his new team, the Toronto Raptors.
The fans were ruthless to Kawhi during the game, chanting "traitor" and booing him almost every time he touched the ball.
At least one heckler recognized Kawhi's mother, Kim -- wearing a Leonard jersey -- and started running his mouth.
You can see in the video, Kim can't take it and starts yelling back -- "A**hole, shut up!" -- all while continuing to eat her snack ... without spilling a drop!
Unfortunately for Kim, the Raptors ended up losing the game ... 125 to 107. Kawhi put up 21 points and 5 assists.
Kawhi’s mom was ready for all the smoke from Spurs fans 😤
(via @@davidmfajardoo)pic.twitter.com/jQz52xjNsp