Pete who? What’s the origin of this exclamation?
St. Peter. It’s a euphemism for “For God’s sake” from a time when it was considered blasphemous to use God’s name that way.
The euphemism only arises around the 1890-1910 period. It could be “for the love of mike” “for the love of Pete” or “for Pete’s sake.”
I thought the expression was originally “For pity’s sake.” No?
Isn’t Peter also the guy that checks people in at the “Pearly Gates of Heaven”. You know the guy who you see on the cartoons with the huge book of people’s names in them and the long line of recently deceased people standing in front of him?
The premise I always got is when somebody says that to you they want you to stop becuase they either a.) want you to stop something that could quite posibly get you killed (even if just metephoricaly) thus causing a harder work load on good ol’ saint Pete or b.) Stop doing whatever sinful act it is you are doing so saint Pete doesn’t have to send you to hell.
This is what my “Mommy” told me anyway.
Yes. This comes from a passage in the Gospels where Jesus says to Peter that he gives him the keys to the Kingdom of Heaven.
Great catch on your part! The expression “For pity’s sake” is used frequently in print in the 1840-60 period. And no one seems to think anything about it.
Was there some variant in common usage prior to 1840?
Probably so, but no need. The OED shows this one back to the 1500’s. My newspaper database just doesn’t reach that far back. 
But it would be interesting to know what parallel euphemisms were about.