The adverb toot sweet means straight away, immediately.
It represents humorously, after toot and sweet, an anglicised pronunciation of French tout de suite, of same sense.
Before the First World War, it was only used in representations of French speech.
One of its earliest occurrences is in Sharpe’s London Magazine: a journal of entertainment and instruction for general reading. In its March 1848 issue, an article titled Galloglossia criticises the way “John Bull must discard his honest, straightforward, manly language, and adopt in its stead the mincing and distorted speech of his [French] neighbours”:
In the days of stage coaches we heard in the coffee-room of an inn much frequented by those creeping vehicles, a good stout representative of our insular greatness shout “Garsong!” and a clumsy, greasy waiter respond “Toot sweet, Mounseer !”
During World War One, toot sweet became part of the British soldiers’ slang. As an appendix to his 1917 account of his war experiences, titled Over the Top, by an American soldier who went, Arthur Guy Empey wrote Tommy’s dictionary of the trenches, in which he included:
“Toots Sweet.” Tommy’s preach for “hurry up,” “look smart.” Generally used in a French estaminet when Tommy only has a couple of minutes in which to drink his beer.
The expression also existed in the form toot and sweet. For example, Nevil Shute Norway wrote, in his 1942 novel Pied Piper (the story of an old man who rescues seven children from France during the Nazi invasion):
Get them kids dressed toot and sweet — I ain’t going to wait all night.
The phrase the tooter the sweeter is an alteration of the sooner the better after toot sweet.
It is typically used to intensify a preceding use of the positive form.
It is first recorded in the 5th December 1917 issue of the British weekly magazine of humour and satire Punch, or the London Charivari. The following cartoon has this caption:
The new language
Tommy (to inquisitive French children): ‘Nah, then, alley* toot sweet, an’ the tooter the sweeter.’
* alley: for allez!, go away!