As high as a kite
Highly excited, or under the influence of drink or drugs.
In 1930s USA, 'high' began being used to mean 'under the influence of drugs' and that usage spread to the rest of the English-speaking world during the hippie movement of the 1960s. The word had previously been used for centuries with the same meaning but with reference to drink rather than drugs. An example of that usage is found in Thomas May's 1627 translation of the 1st century Roman poet Lucan's Pharsalia:
He's awash with rich dishes, high with wine.
Despite the fact that 'high' was used to mean 'intoxicated' and that 'as high as a kite' is now also used to mean 'extremely intoxicated', it is the more prosaic use of 'high', that is, 'far above the ground' that is the source of this phrase.
In both the UK and USA in the mid 19th century, 'high as a kite' began being used and it's meaning was entirely literal, that is, it meant 'high off the ground'. Early citations from both places are:
- In the Ohio newspaper The Elyria Courier, June 1853:
All I can say is that the Herald has an abiding affection for the Whig party and is going to fly that flag "as high as a kite".
- In the London Daily News, January 1871 (in a report of the Prussian siege of Paris):
If you can hold out till March that Prussians will be knocked up as high as a kite.
The expression didn't become established in the USA and was rarely recorded there again until the mid-20th century, by which time 'high' was certainly used there to mean 'intoxicated'. The lack of any continuing use of the phrase in the USA seems, to me at least, to point to a UK origin.
Moving back to 19th century England we have two candidates for the 'kite' part of the phrase - either children's toy kites or the bird of prey of the falcon family, commonly called the Red Kite. These latter kites were very common in mediaeval England and often make high soaring flights looking for prey. This is the family of birds that Shakespeare referred to as 'Hell-kites' when he coined the term 'at one fell swoop'. It would seem that red kites have the right credentials to be the source of an English figurative phrase. However, red kites were persecuted and disappeared from England in the early 1800s. It would be odd for someone coining a phrase in the mid 1800s to choose to refer to a bird that they had in all likelihood never seen. It seems more likely, although difficult now to prove, that 'as high as a kite' wasn't inspired by a befuddled falcon but by a children's toy on a string.
See other 'as x as y similes'.