Jossip reports that NBC’s David Gregory recently “mouthed off” to a waitress in front of Tim Russert — and Russert was apparently infuriated by the newsman’s diva-like behavior, telling him “never to behave that way in front of him again.” A tipster now tells Big Head DC that Russert vented about the incident to frequent MSNBC pundit Mike Barnicle who told the NBC staffers who leaked to Jossip. Lesson here: Be kind to the help, kids.