“Musically, Dylan’s not very gifted; he’s borrowed his voice from old hillbillies. He’s got a lot of borrowed things. He’s not a great guitar player. He’s invented a character to deliver his songs … it’s a mask of sorts.” Why would Mitchell be so gruff with an icon? Likely because he didn’t show her the respect she deserved.
The two have shared the stage on countless occasions
Source: When Joni Mitchell labelled Bob Dylan fake and a plagiarist