Feint: You can use Bluff to feint in combat, causing your opponent to be denied his Dexterity bonus to his AC against your next attack. The DC of this check is equal to 10 + your opponent's base attack bonus + your opponent's Wisdom modifier. If your opponent is trained in Sense Motive, the DC is instead equal to 10 + your opponent's Sense Motive bonus, if higher.
Should feinting an opponent in combat, also remove their dexterity from their CMD? It says in the rules only their ac, but it also makes sense that one would feint before a grapple, or a trip attempt to help throw their opponent off guard.
If your next attack is a combat maneuver, then yes.