The dreaded Murphy

It is unclear to me why humans are so adamant to never utter these phrases. When one of them inevitably does the group will usually attempt to stop them before they finish. When pressed, they stated it would invoke some human law owned by a "Murphy". I didnt get it, but I am compiling a list to disseminate to the officers of phrases that are not to be uttered prior to or on any missions.

So far I have:

"Oh man, I hope we finally see some action"

"This is my last sortie before retiring tomorrow"

"It'll be a standard mission, by the book"

What more lines?