Sorry, Logan Paul, you ain't gettin' a crack at CM Punk in the UFC Octagon -- Punk just slammed the door on the possibility ... and then dissed the YouTube star for good measure.
Logan's brother Jake Paul had been lobbying Dana White to make the fight happen -- claiming Logan is a real athlete who could compete with guys on the UFC roster, including Punk.
In fact, Joe Rogan said he was impressed with Logan's talent during his boxing match with KSI earlier this year .