John Mayer is dissing fellow songwriter Taylor Swift! The "Half of My Heart" singer says Swift's song "Dear John" made him "feel terrible."

The country song was written after Swift's failed romance with Mayer. In an interview with Rolling Stone, he explains why he was upset after the song was released. John says:

    "Because I didn't deserve it. I'm pretty good at taking accountability now, and I never did anything to deserve that. It was a really lousy thing for her to do."

Ouch! Mayer, who says he "never got an email ... I never got a phone call," adds:

    "I was really caught off-guard, and it really humiliated me at a time when I'd already been dressed down. I mean, how would you feel if, at the lowest you've ever been, someone kicked you even lower?"

As for his thoughts on her songwriting talent, Mayer goes on to say:

    "I will say as a songwriter that I think it's kind of cheap songwriting. I know she's the biggest thing in the world, and I'm not trying to sink anybody's ship, but I think it's abusing your talent to rub your hands together and go, 'Wait till he gets a load of this!' That's bulls**t."

How do you REALLY feel, John?