Some things men can say when getting caught looking at another woman:

• "I can't believe that outfit she is wearing"; (said disdainfully).
• "Look at that guy!... Over there... behind the woman."
• "I think that's a man dressed as a woman!"
• "Isn't that the actress from the movie Delicatessen?" (Chances are she hasn't seen that movie - and neither have you, but you will get brownie points naming a foreign film, and it will be just obtuse enough to distract her.
• "I think that's the girl I knew from high school who eventually joined a convent (or was committed to an asylum) and turned out to be a real nut case."
• "Help me, I got something in my eye... can't see a thing!"
• "Hey that's the loser I dumped in order to go out with you. Boy am I glad I ever got away from her. What a moron."
• "I was just thinking how I felt sorry for her - since she can never hold a candle to you!" (This one might only get you punched, but its worth a try.)
• "Do you think she's prettier than me?" (Give her a taste of her own medicine!)