Donald Trump Rips Bill Maher -- How Dare You Insult My Parents!

Donald Trump has made it clear ... his legal war with Bill Maher isn't just about the money ... it's personal -- telling TMZ the comic CROSSED THE LINE when he suggested Trump's mom banged an orangutan.

Trump just appeared on "TMZ Live" and explained why he's confident he'll emerge victorious in his $5 million lawsuit against Maher ... claiming he doesn't believe Bill was joking when he appeared on Leno earlier this year and challenged Trump to prove he isn't the "spawn of his mother having sex with an orangutan."

Donald says he vows to defend his parents' honor -- telling us, "What he said about my father is disgraceful ... and what he said about my mother, who's deceased, was in a certain way, even more disgraceful."

"I've never heard anything like that said about my parents ... who were truly great people."