What is the origin of the exclamation "For Pete's sake!"?

Question

I say it often enough, you'd think I knew what it meant!

Answer 1

It's another euphemisms "for God's sake". As Saint Peter kept the keys to heaven, using his name was probably less sacrilegious then using God's.

Answer 2

It's probably a reference to St Peter, founder of the Christian cult. I guess people thought saying "for Christ's sake" was kinda blasphemous.