DeMarcus Cousins lost his cool ... twice ... and it cost him.
The NBA has fined the New Orleans Pelicans star $50,000 after footage surfaced showing him telling a fan to "suck my d**k" during Sunday night's game against the Lakers.
The league also references an incident where he told a heckler the following night to "sit your fat ass down."
On both occasions, Cousins was being heckled by rival fans. Both were away games.
Don't cry too much for DeMarcus ... he's making $16.9 MILLION this season.