Do you ever?

Do you ever wonder when you are in a large crowd or see a large crowd of people, think to yourself...this would be the perfect time for terrorists to knock out a large number of people?

I had this conversation at work with a co-worker and she says that she thinks this too. My boss overheard us and told us we were crazy and we shouldn't waste our time worrying about such things. It's not that worry, but I think about it. For example, how perfect would it be for someone to drop a bomb on us or have a shooting spree when we are downtown watching the fire works. The fireworks in Detroit draws a crowd of over a million people, it is loud, it kind of chaotic...no one would even know what hit them. We are all too engrossed in fireworks show and taking in the sites, that would we even know what hit us?
I know I am probably a little weird, but does anyone else feel like this? Do you ever think about it?
Let me know...My Co-worker and I can't be the only one's.