Tyga must have a lot on his mind, because he apparently forgot he was supposed to perform Friday night in San Diego ... and the fans were enraged.
Kylie's ex-BF was supposed to perform at Omnia nightclub, and the event was pricey -- $100 for men and $70 for women, and that's just to cross the threshold.
As the night wore on, people figured out what was up and things got rowdy. Eyewitnesses tell us there was pushing, shoving, bottles and glasses were thrown on stage, etc.
The DJ tried to vamp up the crowd from midnight until 1:45 AM, but they weren't having it.
It looks like there may be an issue with refunds, because management told the crowd, "Nothing could be done."
Check out Tyga's apology ... no excuses, and generally "sorry" doesn't cut it.
Tyga's next performance is Saturday night at the FivePoint Amphitheatre in Irvine, CA for the Powerhouse Liftoff Edition, but clearly ... don't hold your breath.
By the way, check out our story about Tyga and his connection to Tristan Thompson and the Kardashians, proving the Kevin Bacon "six degrees of separation" theory.