In music, a segue (pronounced SEG-way) is a smooth transition from one section to another. As evolved from seg fault, I coined this exclamation to refer to situations where someone says something completely off topic from the thread at hand (see: context.dll missing or not found). In particular, I use it when someone starts off by saying something like"speaking of which, that reminds me...." and then proceeds to say something which doesn't even remotely fulfill the relevancy suggested by their first statement (see: Bryce). For example:
Okay, that example never happened. But it could have. And if it did, that's how this expression would be used.