When one man proceeds to cum into the anus of another to which he follows up by fisting the asshole using semen as lub.
While on the bus Joshua exclaimed to his friend Jennifer, I'm not huge on anal but I'd be up for cum-fisting all night.
by Tsx Weasel July 27, 2016

In a 69 styled position, when you punch your girl in the asshole as she is climaxing, and you get a bunch off poo on your fist.
Man I was hoping she wouldn't climax yet, so I pulled out the ole poopy fist on her , little did I know she had a large chilli and enchilada lunch.
by pussycat93 December 25, 2016

Same theory as Schroeder's Cat, if you're blindfolded and fisting. You do not know whether you are fisting a vagina or a rectum until you remove the blindfold.
Have you heard of Schroedinger's Cat?
No, but have you ever heard of Quantum Fisting? Great time at my stag party.... I think.
No, but have you ever heard of Quantum Fisting? Great time at my stag party.... I think.
by Quantosexual December 7, 2018

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