Now, Cuban is firing back ... telling us Trump's allegations are "funny because I never golf. Never. 1x in my entire life."
Cuban says he does have a membership to Dallas National -- "The nicest club in Dallas" -- but says he's literally never been there.
Mark did give us a message to pass along Trump -- "Donald, I'm glad you got the chance to watch me golf. Where? If you want to know the real story about my golf game, call my club, Dallas National and see what they have to say ..."