You're probably thinking about some app not being able to start when some other specific app is running because both were using a GUID copied from SO for implementing single-instance apps.
I cannot find the source, but the folklore says a Linux kernel developer wrote a USB tutorial with his USB VID/PID, years later, he found he became the manufacturer of all sorts of gadgets he never heard about.
It's a good example but I think it's not exactly that. Maybe it was a GUID generation code that would generate the same one for every instance?
> I know it has something to do with some mythical thing called a mutex, rarely can I find someone that bothers to stop and explain what one of these are.
Possibly the SO question in question: https://stackoverflow.com/a/522874/615306