I didn't either at first, I went and looked it up after enough people started using it to nullify/discredit what I had to say in serious conversation.
Murphy's Law Book 2, January 24, 1980
A book of jokes, meant to be humorous.
No previous literature related to it before then.
I can't help but laugh when people use it now, so I guess its still funny... in a way.
It says a lot about the character of a person that takes a joke and uses it in a way, that it was never intended to be used. Useful knowledge to keep in your back pocket if needed.
It was a joke in a joke book, and has been taken entirely out of context by most people who use it to justify anything.