Wordorigins.org

A dry run is a rehearsal. The term appears to come from American firefighting jargon, where dry denoted a practice where the hoses were not turned on.

Run, meaning a response to a fire alarm, either real or a drill, dates to the late 19th century. The Portland Morning Oregonian of 11 September 1886 contains a use of wet run in reference to a contest between fire companies:

Open to all; wet run; distance, 200 yards to hydrant; lay 350 feet of hose; [...] ; attach pipe and throw water.

This is a rather common American slang phrase. Those who drink the Kool-Aid exhibit unswerving loyalty to and belief in their leaders. This figurative use has been around since the mid-1980s.

Kool-Aid is a brand name for a soft drink mix that is popular among American children, but the allusion is actually a much grimmer one. In 1978, Jim Jones, the leader of the People’s Temple, a San Francisco cult that had recently moved to the jungles of Guyana, ordered his people to commit suicide. 914 cult members died, including 276 children and Jones himself. Most killed themselves by drinking a grape drink laced with cyanide and sedatives. (It may not have actually been Kool-Aid brand that was used, but as the most popular brand that was the name that stuck in the public consciousness.) Most of those who refused to commit suicide were executed, either shot or killed with lethal injection.

Hence, to drink the Kool-Aid is to show cult-like devotion to one’s leaders.

This is a rather etymologically mysterious term to most people today, but an examination of the changes in meaning of drag over the centuries makes it clear why we call racing for fastest acceleration drag racing.

In the 16th century, drag was a term for a sledge, a platform with skids, not wheels, that could be dragged behind a horse or ox. From an act of Elizabeth I of 1576:

Sleades, carres, or drags, furnished for...repairing...high wayes.

These two interjections have both been popularized by cartoons.

The first, doh, has been made famous by Homer Simpson, but he was not the first to use it. That honor goes to James Finlayson, who appeared with the comedians Laurel and Hardy in several films. This dialogue is from the 1931 Pardon Us, Laurel and Hardy’s first full-length film:

Professor Finlayson: How many times does three go into nine?
Stan: Three times.
Finlayson: Correct.
Stan: And two left over.
Finlayson (to Ollie): What are you laughing at?
Ollie (snickering): There’s only one left over.
Finlayson: D-ohhhh!

Triskaidekaphobia is the fear of the number thirteen. It began life, and has pretty much remained, a psychological jargon term. Its first appearance in English is in Isador Coriat’s 1911 Abnormal Psychology.

Like many scientific terms, this one is a modern invention based on Greek roots. Triskaideka, or τρεισκαιδεκα, is Greek for thirteen, to which the suffix -phobia, or -φοβία, meaning fear, is added.

(Source: Oxford English Dictionary, 2nd Edition)