From the 1811 Dictionary of the Vulgar Tongue - B

BACKED. Dead. He wishes to have the senior, or old square-toes, backed; he longs to have his father on six men's shoulders; that is, carrying to the grave.
BANG UP. Quite the thing, hellish fine. Well done. Compleat. Dashing. In a handsome stile. A bang up cove; a dashing fellow who spends his money freely. To bang up prime: to bring your horses up in a dashing or fine style: as the swell's rattler and prads are bang up prime; the gentleman sports an elegant carriage and fine horses.
BAPTIZED, OR CHRISTENED. Rum, brandy, or any other spirits, that have been lowered with water.
BARKING IRONS. Pistols, from their explosion resembling the bow-wow or barking of a dog.
BATCHELOR'S FARE. Bread and cheese and kisses.

BEAU-NASTY. A slovenly fop; one finely dressed, but dirty.

BEAU TRAP. A loose stone in a pavement, under which water lodges, and on being trod upon, squirts it up, to the great damage of white stockings; also a sharper neatly dressed, lying in wait for raw country squires, or ignorant fops.

BINGO BOY. A dram drinker.

BLACK FLY. The greatest drawback on the farmer is the black fly, i.e. the parson who takes tithe of the harvest.

BLACK SPY. The Devil.

BLOWER. A pipe. How the swell funks his blower and lushes red tape; what a smoke the gentleman makes with his pipe, and drinks brandy.

TO BOX THE JESUIT, AND GET COCK ROACHES. A sea term for masturbation; a crime, it is said, much practised by the reverend fathers of that society.

BRISTOL MAN. The son of an Irish thief and a Welch whore.

BULK AND FILE. Two pickpockets; the bulk jostles the party to be robbed, and the file does the business.

BUTTER BOX. A Dutchman, from the great quantity of butter eaten by the people of that country.