Photogs caught up with the star at LAX Thursday ... and, with the election just two weeks away, we had to ask the controversial actor who would be getting his vote.

Mel laughs it off at first ... saying he doesn't think it's any secret who he's voting for -- and confirms he's backing Donald Trump for a second term over the current vice president.

He doesn't say what he thinks America will look like under a second Trump term ... but, he says he knows it won't be good if Harris takes the U.S.A.'s reins.

Take a listen for yourself ... Mel blasts Kamala over what he sees as a lackluster track record and says she hasn't laid out any serious policies. That's when Mel goes for the jugular -- saying Kamala's got "the IQ of a fence post."

This echoes something Trump has said repeatedly about Harris ... saying she's mentally unfit to be president and later calls her both mentally impaired and disabled.

Mel has been known for his controversial statements... having spouted off racist, sexist and antisemitic comments in the past -- and, it looks like he's not caring what anyone thinks about his new diss of the VEEP.