We'd recognize John Mayer from a mile away, but one clerk at Circuit City in Santa Monica, Calif., sure didn't! The crooner and his new GF, Minka Kelly went to the store and picked out $400 worth of merchandise recently. When John pulled out his American Express Black Card (whoa, big spender!), the employee asked to see ID, but John didn't have his license on him, a spywitness tells Us Weekly. "I actually lost my ID and don't have one," John said, so the Circuit City clerk "advised John he would not be able to buy anything." But instead of throwing a divalicious tantrum, "John was so embarrassed," the onlooker says. "Minka was smiling and giggling and rubbed his back in support." Then, the employee had a total "duh!" moment, recognized who John was (wouldn't the name on the credit card tip him off?), and put the purchase through, while apologizing for the mistake. "John and Minka laughed and said it was no big deal before they paid and left the store holding hands," reports the source. Aww! Someone's tamed the wild Mayer!