I agree with the surprise suggestion from skullboy. I dressed myself as a scarecrow one year laid out on the porch. The look was made better by wearing a real pumpkin on my head (carved from the bottom) which made me look even more like a stuffed dummy.
I'm a big fan of misdirection, such as coffin scenes that open from the bottom when all attention is at the head. That's just one example. What if you have someone hidden within the front porch scenery that only jumps out once they are off with the treat (thinking they're off to the next house)?
How about a leaf blower or shop vac on a remote with the blower tube disguised in some decorations (something like corn stalks) that will be close to their face? The noise and gust of air should really catch them off guard.
For the teen girls you could come up with a haunt for them specially, with the things they are afraid of, like fatening mirrors. It's like the haunting story in the Addams Family Values: "The next morning, when the campers woke up...all of their old noses had grown back!"
I think I could come up with some more for that problem. As to the tough guys; I have the same problem: metalheads. Completely incapable of getting scared...
If your using scareactors either use a calm soothing type voice at first then hit them with a pissed off drill sargent yell, works well with my crew. If not, the art of surprise can be your best friend. Just don't do it to everyone, keep them wondering as to what triggered the scare. Also you can mess with them mentally using different types of sound, smells and sight effects.
In all our years, we've had very few of what I would call "Tough Guys", the bored, been-there, done-that adolescents, if that's what you're refering to. We do nothing different with individual groups going through, but we try to "tame it down" for smaller kids. They may enter all pretentious, but if you put on a good enough production, your guests drop all pretenses.