Mel Gibson has at least one supporter in Hollywood ... his friend Mickey Rourke ... who tells TMZ, he thinks Joe Eszterhas is a LIAR ... who's out to smear Mel's reputation.
Mickey was leaving Caffe Primo in West Hollywood when we asked about Joe's allegations that Mel is a violent Jew-hater who hates John Lennon.
Mickey's response -- "Everybody is looking to make Mel look bad ... he's an easy f**king target."
He explained, "We live in a town that's built on envy."
It's not the first time Mickey's come to Mel's defense -- back in 2010, following Oksana Grigorieva's domestic violence allegations, Mickey said, "I wouldn't believe everything you hear ... I think he's a good dude, you know. And ah, screw the bitch!"