Parents who bring their small children into the gift shops of zoos (or other such places) and look around, and then say, "We're not getting anything. Don't touch."
Okay, yeah, keep your kids' grimy hands off the merchandise, but how can you possibly think it's fair for you to drag a tired and hungry four year old into a room filled to bursting with toys and then say, "You can't have any of it."
Why would you tease a little kid like that? If you're not willing to spend any money, don't drag your kids into toy stores!