Bristol Palin -- Sued By Bar Heckler

He told Bristol Palin her mother was "evil" and a "whore" ... but now the man who verbally accosted Sarah Palin's daughter in a Hollywood bar last year is suing Bristol for defamation.

It's all over that infamous encounter at Saddle Ranch on the Sunset Strip back in September ... when Stephen Hanks shouted at Bristol, "Your mother's a whore" (clip below -- skip to 1:40).

Hanks is pissed because he claims the incident was captured by a reality TV crew that was with Bristol. Hanks says he never signed a waiver ... and was furious when his image started appearing in ads for Bristol's new Lifetime show, "Bristol Palin: Life's a Tripp."

In his lawsuit, filed in L.A. County Superior Court, Hanks claims Bristol later gave an interview to a gossip mag and blamed him for causing her to leave Los Angeles and move back to Alaska.

Hanks claims he can PROVE Bristol was lying ... because she had already purchased a new home in Alaska two months before their encounter.

Hanks says Bristol's statements to the gossip mag hurt his reputation and damaged his career.

In the suit, Hanks also gripes that Bristol accused him of being gay during their encounter -- saying she could "tell" by the way he looked.

Hanks is suing Bristol and A&E -- the company behind Lifetime. He's asking for unspecified damages.