KATIE Holmes is no snob. Even though her downtown apartment building has been deluged by paparazzi since her Broadway debut in “All My Sons,” she took time to make an appearance at the low-key Christmas party in the building’s lobby. “She was very nice, even though she always has the bodyguard with her,” said our spy. “She only stayed for about two minutes to make small talk with some of her neighbors on the way to her waiting SUV.”