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1 definition by mitch aka titch

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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