Michael Lohan -- RIPS Dina Lohan ... She's Hiding Something

Whyyyyy wouldn't Dina Lohan take a lie detector test on national television? Because she's a liar who has something to hide ... so says Michael Lohan.

Our photog spotted Lindsay Lohan's dad at LAX on Friday and asked him all about the nuclear fight he had with Dina ... after their appearance on talk show called "The Test" turned into an all-out bash fest.

As TMZ previously reported ... Michael and Dina went on the show -- which utilizes lie detectors and DNA tests to help guests resolve conflicts -- to hash out their past. Michael submitted to two polygraphs, while Dina submitted to zero. Each side left the show pissed off and accusing the other of lying.