Example: For the love of Pete, can we just pick a restaurant and stop searching? I am hungry.
Origin: This phrase and phrases like "for Pete's sake" are euphemisms for the phrases "for the love of God/Christ" or "for God's/ Christ's sake" and hail from a time when those phases were considered blasphemous. Nowadays phrases like "for the love of god" are commonly used, but the euphemisms are still used.
Why Pete? Most likely it is a reference to the catholic Saint Peter.
Other phrases with similar origins are: "Zounds!" (archaic British slang), is a contraction of "christ's wounds", "oh my goodness" and "oh my gosh" for "oh my God", and "gosh darn it" for "God damn it"