i'll be a monkey's uncle - You say this when you're so surprised you swear you can smel

You say this when you're so surprised you swear you can smell a monkey's butt from ten miles away.

'You just got a perfect score on the test? I'll be a monkey's uncle!'

'He ate the last donut? I'll be a monkey's uncle!'

'You broke my phone? I'll be a monkey's uncle!'