In Shakespeare's time the word 'butt' referred to the casks in which wine was stored and 'buttery' was the room in which the 'butts' or the casks of wine were stored. The 'buttery-bar' was a shelf attached to the lower portion of the door of the 'buttery' which was split horizontally. The person who dispensed the wine to those wanted a drink placed the full cups of wine on top of the shelf, the 'buttery-bar.'
In Act I Sc.3, Sir Toby Belch the uncle of Olivia brings home Sir Andrew Aguecheek to be introduced to Olivia. He advises Sir Andrew to befriend Maria the maid of Olivia so that he can gain access to Olivia. Maria knows fully well that Andrew is an impotent fool and she mocks at him when he fails to comprehend and respond immediately to Toby's command to "accost" her, meaning to make love to her. It is then that she teases him in the following manner when he challenges her:
Fair lady, do you think you have
fools in hand?
MARIA:Sir, I have not you by the hand.
SIR ANDREW:Marry, but you shall have; and here's my hand.
MARIA:Now, sir, 'thought is free:' I pray you, bringyour hand to the buttery-bar and let it drink.
Maria teases the impotent Sir Andrew by placing his hands on her breasts (in medieval slang, "buttery-bar" referred to a woman's breasts) knowing fully well that he is incapable of any sexual advances and insults him by telling him to go get himself a drink at the "buttery-bar"of the house.