Green’s Dictionary of Slang

1. (US Und.) a long and epic poem, often trad. in prisons.

a.1954		‘Mexicana Rose’ in D. Wepman et al. Life (1976) 43: That’s the end of my toast, there’s no more to be said.
1964		R. Abrahams Deep Down In The Jungle 51: Many of them take the form of rhymes or puns, signaling the beginning of the bloom of verbal dexterity which comes to fruition later in the long narrative poem called the ‘toast.’ [Ibid.] 147: If anyone asks you who pulled that toast, / Just tell them old bullshitting Snell from coast-to-coast.
1974		B. Jackson Get Your Ass in the Water 3: Toasts can be told anywhere — at parties, lounging around bars and streetcorners, on a troopship crossing the boring ocean — but they seem to be told in county jails more than anywhere else.
1987		D. Hebdige Cut ’n’ Mix 124: Yellowman [...] began to develop his famous pornographic slack toasts.
1990		S. Morgan Homeboy 95: Top Dog took up the toast. ‘Now one day Dolomite took a stroll.’.

2. (US) the best, the finest, anything outstanding [i.e. that which deserves a SE toast].

[1785		Grose Classical Dict. of the Vulgar Tongue n.p.: Toast, [...] a beautiful woman whose health is often drank by men. The origin of this term (as it is said) was this: a beautiful lady bathing in a cold bath, one of her admirers out of gallantry drank some of the water: whereupon another of her lovers observed, he never drank in the morning, but he would kiss the toast, and immediately saluted the lady].
1984		Eble Campus Sl. Mar. 1: bad as toast – amazingly good or shocking: Those girls in their bikinis were as bad as toast.