Bristol Palin -- I'm No Homophobe, I Was Just Defending My Mom

There's nothing homophobic about Bristol Palin's heated exchange with a heckler last night -- according to her rep ... who claims Bristol was only defending her mom, Sarah Palin.

A rep for Bristol tells TMZ, she "was approached in a confrontational and inappropriate manner when two men aggressively shouted expletives aimed at her in reference to her mother. Bristol responded to the unprovoked verbal assault by calmly standing her ground and defending her family."

As we previously reported, Stephen Hanks yelled, "Your mother's a whore" -- prompting a face-to-face argument during which Bristol shouted at Hanks, "I just know you are" a homosexual.