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1.
A personal conjecture towards another informing them that you do not believe what they are saying. A way of telling someone that what they are telling you is a big steamy pile of smelly bullshit. Hence they would be "full of shit".
someone - "I am such a badass I fended myself from four bears last year after we got lost on the canoeing trip"

you - " You are full of shit."
by Didnt use my real name November 08, 2010