“The interesting thing is just how insecure and socially inept she is,” the eyewitness told us after the party. “She walked around the garden most of the night pretending she was speaking to someone on her cell phone.” Apparently, Ms. Hilton, 26, barely put her bejeweled Sidekick down the entire evening, even when she was quasi-mingling with her fellow partygoers. Our source added that the hotel-chain heiress was trailed all evening by “a security guard and some weird guy in a strange Halloween-style hat.”