'he is so full of himself'
What does the phrase "You're so full of it!" mean?
Maybe something like "You're crazy." ?No, not really 'crazy'. Here the word 'it' substitutes for an impolite word. See
www.phrases.org.uk bulletin_board 22 messages 599.html
It occurs to me that you may also be interested in a similar phrase but with an entirely different meaning; see