Jennifer Aniston warned about John Mayer

Jennifer Aniston is being warned off John Mayer by the singer's pals who say he has "a reputation for crushing the girls he's with."

The former 'Friends' actress dined with Mayer this past weekend -- and by all accounts, they were getting very cozy! "They were looking into each other's eyes," an eyewitness said. "It was definitely a date!"

But a source close to John insists that "It's a very new thing. They're still in that 'getting to know each other' phase."

But John's friends are warning the 39-year-old actress to be careful with her latest beau, because he has a long track record for leaving women heartbroken. "Girls fall for him hard because he's charming," OK! magazine quotes a source as saying, "but he has a reputation for crushing the girls he's with."

Jessica Simpson and actresses Minka Kelly and Jennifer Love Hewitt are just a few of the women John, 30, has dated.

"He came on so strong at first," a pal of Jessica's said. "He wanted to be with her every moment. When he wasn't physically with her, he was texting her — but all of a sudden, he got bored and stopped returning her calls."