Crowd Tactics( Races of Destiny, p. 156)
You are adept at moving through and fighting in crowds.
The Crowd Tactics feat enables the use of three tactical maneuvers. You only gain these benefits if the crowd is indifferent or friendly.
Moving with the Flow: Entering a square with a crowd in it does not cost you extra movement.
One with the Crowd: You gain a +4 bonus on Hide checks made in square with a crowd.
Master of the Mob: You gain a +4 bonus on Diplomacy or Intimidate checks when attempting to direct a crowd.
See page 100 of the Dungeon Master's Guide for rules on crowds.