OK... This should be a fun one.

What is the worst mistake you have ever made when doing code? I'll be the first to step forward and admit my mistake.

I was working on an internet shopping cart application. And when adding the total of the order up I forgot to declare the cost of one item as an integer and it defaulted as a string. Well when the total got added up it ended up combining the two values as a string instead of a number. So 400+20 would end up equaling 40020 instead of 420. This bug went on like this while the site was up live for about a week before I noticed. What an embarrassment. But I think it happens to the best of us.

Now who else will step forward and admit their mistakes?