"I just feel like I don't need to be another notch on his belt," she said on Ryan Seacrest's KIIS-FM radio show Tuesday.
But there's no hard feelings.
"I think he's a really nice guy…" Cavallari, 22, said of the singer, 31, who has had flings with Jennifer Aniston, Jessica Simpson and Minka Kelly.
Cavallari says she hasn't sworn off Mayer for good.
When told by Seacrest's sidekick Ellen K that Mayer – whose fourth album, Battle Studies, drops Nov. 17 — is "amazing in the bedroom," Cavallari teased, "I've heard that. Maybe I should give him a phone call!"
Cavallari, whose been "single for almost two years," said she loves her independence. Said the reality star, "I don't need a man."
She also cleared up rumors that her reality foe Audrina Patridge makes more money than her. (The Daily Beast reported she earns $90,000 per episode; Patridge gets $100,000. )
"Well, I can tell you that's not true … that she makes more money," Cavallari said, declining to state her salary.
She said she is "really excited" for the MTV show's sixth season.
"It's fun to be the bad girl," she said. "It's better to be the bad girl than little Miss Sweetheart."
For access to all our exclusive celebrity videos and interviews – Subscribe on YouTube!