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1.
An aged but well maintained car, generally from the 1980s, that has been bought cheaply and lovingly restored to its former glory. Rusty Monkeys are typically bought cheaply (for less than £500) and restored to take part in charitable events, races, meetings or just for the fun of it.
Typical and popular Rusty Monkeys include the Audi Quattro, the old-style Ford Escort, the Ford Scorpio, the Trans Am and the original police Panda cars like the Ford Anglia.
by bravebrian November 18, 2010
 
2.
Drinking down a forty ounce alcoholic beverage to a desired level (typically the bottom of the cone), then topping off your forty with Mad Dog 20/20. The same concept as a brass monkey, but a lot more disgusting.
Jose: That beezy was on my dick last night!

Juan: Well no wonder, she had herself a rusty monkey
by grady hernandez October 13, 2012
 
3.
While in the act of receiving a blow job, the man sharts in the females face. Spray poo might be involved
Example: "I was totally getting some head and I gave this chick a rusty monkey... Sharted right in her face"
by oops I pooped February 25, 2010