I found this thread once when I was looking through the old (really old) forums, and I figured now is a good time to bring it back since... well, you know.
You know you've played too much Lemmings when...
You tell people that your house was built using the brick tileset.
Your standard response when someone asks you for help is "Just a minute!"
You keep a bear trap and 10 ton weight handy, just in case.
You have a flashing "OUT" sign above your front door.
and, of course...
You take a week of in an attempt to preserve your sanity.