When is a bug not a bug?

This is a question I ponder as I prepare to launch my site. How many times have I checked and recheched all the functionality only to find that a bug we thought we'd exterminated has popped back up. Well, I got my friends to test the site and I have established a new statistical norm - when you get 4 good friends to test something for you, one will promise to do it and go surfing instead, one will get logged out on the first page, one will click on two pages and fail to understand a single aspect of the site and one will give you good feedback. I suppose this is why we call them friends, not employees. I am getting ready for the second phase of feedback which will come several months after live launch when I guarantee all four friends will say 'Yeah I had that problem too' shortly after the first live meltdown. Anyway, back to that little bug in the system ... my lead developer has promised to eat a hat if it reappears so I'm dusting off my old riding hat in preparation. And the whip. Still 7 days from launch. Will report again when I'm ready to go.