Most of us are not perfect. (Well, except Jon Skeet)

Have you made a terrible mistake that you would like to share? The idea is that we could all learn from our mistakes and by collecting them together here, we can avoid some common ones and discover some no-so-common ones we may have overlooked.

Oh, and this question is CW, of course.

Edit: This question is different than http://stackoverflow.com/questions/1928002/what-is-the-worst-programming-mistake-you-have-ever-seen because we are sharing our own mistakes.

Edit again: And this one http://stackoverflow.com/questions/130965/what-is-the-worst-code-youve-ever-written is different too - it asks for code. My question does not have that restriction!