The act of one sticking their thumb in another's buthole, and then "serving" them their own feces by placing the dirty thumb directly into their mouth. In order to make this "rusty", one may not use lube to help the process.

for added excitement try the "reverse rusty butler": have the person do a headstand so that the thumb is inserted as a "thumbs down".
"After all-you-can-eat tacos, things got hot and heavy off the tequila and I gave her a mad Rusty Butler."

"After yoga class Erin was showing off her new headstand pose when Chris decided to surprise her and slip her the reverse Rusty Butler."
by Frito10 May 09, 2010
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V. The act of performing coitus with an individual wearing a penguin suit in an ambulance.
I received a rusty butler the other day.

My girlfriend and I tried a rusty butler last weekend and now I'm never going back.
by SurferDuck December 22, 2019
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