The metaphor of food served up on a slice of toast is the origin of the phrase to be had on toast and variants, meaning to be cheated, to be swindled.
It is first recorded in The St. James’s Gazette (London) of 6th November 1886:
The judges in the High Court are always learning some new thing. Yesterday it was entered on the record that the court took judicial cognizance of a quaint and pleasing modern phrase. They discovered what it was to be “had on toast.” It was the proprietor of one of the most popular and agreeable hostelries in the Home Counties who was subjected to the process. He has been in the army; he is an innkeeper, a farmer, and a sportsman. Natheless he gave £255 for an animal described as “one of the greatest horses in England.” It could jump anything, walk five and-a half miles an hour, and was (of course) “as comfortable as an arm-chair.” When the purchaser’s faithful ostler saw that horse he made the remark about toast. For it turned out that the greatest horse in England had bog-spavins¹ and curb in one hock, and the highest price that could be got for him at Tattersall’s² was £48 6s., at which price his former owner bought him back. “Such dangers do environ” those that buy horses; in which agreeable pursuit the very wiliest are occasionally “had on toast.”
¹ bog spavin: a soft swelling of the joint capsule of the hock of horses
² Tattersall’s: the main bloodstock auctioneer in the United Kingdom
The same metaphor is the origin of to have someone on toast and variants, meaning to have someone at one’s mercy, to be able to deal with someone as one wishes, and to subject someone to anxiety.
The earliest instance of this phrase that I have found is from The Sporting Times (London) of 7th July 1888:
TALEPITCHER’S IMPROVED ÆSOP.
Nº I.—THE THIRSTY RHINOCEROS.
A thirsty Rhinoceros, having, to his great joy, encountered a Dromedary in the Desert of Sahara, besought the latter animal, of his Mercy, to give him a Drink; but the Dromedary refused, saying he was “bulling”³ the Fluid for an Advance. “Why,” said he, to the Rhinoceros, “did you not imitate my Forethought and Prudence, and take some heed to the morrow?” Of course, he’d got him on toast; the Rhinoceros could only acknowledge the Justice of the Rebuke. Some time afterwards he met, in an Oasis, the Dromedary, who had sold out at the turn of the market, and was now trying to cover his shorts⁴.
“For heaven’s sake,” he gasped, to the Rhinoceros, who was wallowing in the midst of a Refreshing Pool; “trust me for a wet.”
“When I was thirsty,” replied the Rhinoceros; “you declined to stand the drinks. I will not fill you a beaker; but I will give you a horn,” saying which he forthwith proceeded to let the Grateful Sunlight into the Dromedary’s innards.
Moral—Never give a pal the n.f.
³ On a stock exchange, to bull means to try to raise the price of stocks, etc.
⁴ The noun short denotes that amount of stock which a broker who ‘sells short’ needs in order to cover his deficiency; to sell short means to effect a sale of stock or goods which the seller does not at the time possess, but hopes to buy at a lower price before the time fixed for delivery; to cover one’s shorts means to purchase sufficient stock or goods to fulfil one’s contract.