Anyone who has shoved their hand into a friend's sister's cunt
1) WOW I PULLED THE SISTER FISTER ON STEPH
2) I pulled the sister fister on blakes sister
by Zane April 04, 2003

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Top Definition
The act of fisting your sister. Commonly refered to as incest.
Yo this kid named Francis is a fucking sister fister.
by Quay and Justin October 29, 2003

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a brother or even a sister that likes to casualy fist their sister up the vagina or even the arse hole. Most of the time resulting in a very sore vagina/anus, and if caught resulting in a sentence of 10 years in jouvey.
(here is a role-play of a sister fister and his sister)
Kirsten after a long sleep
Kirsten: o hi there Aaron i didnt see you over there in that dark corner.
Aaron: You dont need to see me, you just need to feel me
Aaron and Kirsten both grin and Kirsten turns around
by mitch aka titch June 11, 2006

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Strictly, one who indulges in a particular form of incest, using only their hand (see fister. Often used as a term of contempt, and shortened to "sissy" on account of their unadventurousness.

See also brotherfucker.
Your brother's such a sisterfister, you know.
by Lucifer B August 16, 2005

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The act of fisting your sister. Commonly refered to as incest.
Yo this kid named Nicholas O. is a fucking sister fister!!
by Dankolas O. January 25, 2016

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A person who fists peoples sister
amr fisted my dog
by me March 01, 2004

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A bitch you can stick your fist inside of her pussy, no lube necessary. The word sister referring to any random female.
The girl i met last night i was down to fuck, until i realized it was Sister Fister.
by brando239 November 18, 2008

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