Mod Sun Concert Crowd Chants 'F*** Tyga' After Travie McCoy Drags Rapper

Mod Sun has seriously loyal fans who have his back in the breakup with Avril Lavigne ... and they proved it in NYC with a profanity-laced chant toward Avril's new love interest, Tyga.

Rapper Travie McCoy set it off when he got onstage during Mod's Wednesday night show at Irving Plaza. Before they rocked out to the Gym Class Heroes hit 'Cupid's Chokehold,' Travie called his buddy Mod one of the most loyal dudes he knows.

Seemed to be going in a sweet direction, but then Travie couldn't let the opportunity to blast Avril's new guy pass -- he yelled, "F*** Tyga!"

Mod ran to the back of the stage in shock, but with a big smile on his face ... and then the crowd joined in, chanting Travie's choice of words -- which might perfectly reflect Mod's feelings.

TMZ broke the story -- Avril broke off her engagement last month to Mod Sun just a few days after he kicked off his tour ... and soon after, she immediately started a new romance with Tyga.

We're told Mod was completely blindsided by the breakup -- and that goes double for her quick jump to Tyga.

Mod's fans are doing their best to hold him up.