Fnord
SasqWatch
That's "worst" for you? Wow, talk about different minds. To me that would be the very least of the bugs, hell I wouldn't even notice it.
It's not the worst for me, but it is the most damning, because it is such a basic thing to get right. It's also something that I don't think I've ever seen anyone fail, as learning how to make a program close down properly is one of the very first things you'll learn when you start learning programming.