I had some fun drunks last night... I have a little schtick I do where I talk to a decapitated head that I carry around. The group came through, and I popped out yelling, "Can I have 'em mamma?! Can I have them??", while menacing them with a fake machete. Usually this inspires screams of terror... But in this instance one of the young women in the group said, "Yes you can!" and started trying to give me her phone number!
The point is you just never know how people will react. We want people to be scared, and that is the reaction most of us receive most of the time. However there is always going to be an element of unexpected reaction. That is what makes haunted houses more exciting and fun than movies. The interactivity is what it's all about.