What does "yippie ki yay" mean?

First time John McClane uses that term in the Die Hard series is when he speaks to Hans on walkie talkie. When Hans was asking him if he was another American cowboy inspired by John Wayne and then McClane says he is partial to Roy Rogers and ends his conversation with Yippie Kay Yay and swears after it.

The actual meaning of the phrase from the references I looked up means the phrase doesn't actually mean anything except it's used as reference to an exclamation used by Cowboys in the old times.

An article on The Week.com broke down each part of the phrase:

...But where does the yippee-ki-yay part come from?...Let's break it down.

The yip part of yippee is old. It originated in the 15th century and meant "to cheep, as a young bird," according to the Oxford English Dictionary (OED). The more well-known meaning, to emit a high-pitched bark, came about around 1907, as per the OED, and gained the figurative meaning "to shout; to complain."

Yip is imitative in origin but probably also influenced by the 16th century yelp, which has an even older meaning of "boasting, vainglorious speaking." Yawp is even older, coming about in the 14th century, but now is primarily associated with Walt Whitman's late 19th century "barbaric yawp."

The yips are "nervousness or tension that causes an athlete to fail to perform effectively, especially in missing short putts in golf." As we mentioned in a Word Soup column back in November, some sources, including the OED, cite the first known use of the yips as 1962. However, we found a citation from 1941: "The match consumed three hours and thirty minutes, most of it because Cobb, the tingling-nerved old baseball Tiger, got the 'yips' on many greens and would step back and line up his putts several times per putt."

Yippee came about after yip. The earliest record of this exclamation of delight is from 1920 in Sinclair Lewis's novel, Main Street: "She galloped down a block and as she jumped from a curb across a welter of slush, she gave a student 'Yippee!'" Yippee beans, by the way, are amphetamines.

Yippie with an -ie refers to "a member of a group of politically radical hippies, active especially during the late 1960s." The word, which originated in 1968, stands for Youth International Party and was modeled after hippie.

Now how about the whole phrase, yippee-ki-yay? It seems to be a play on "yippie yi yo kayah," a refrain from a 1930s Bing Crosby song, "I'm An Old Cowhand."

Do cowboys really say this? We're guessing probably not, unless of course they're single-handedly (and shoelessly) defeating a gang of bank robbers on Christmas Eve.

So that's some explanation as to its origin. It's worth pointing out though that Bruce Willis had this to say (in an interview with Ryan Seacrest) about the phrase:

On The Famous “Die Hard” Line Yippee-Ki-Yay…

“It was a throwaway. I was just trying to crack up the crew and I never thought it was going to be allowed to stay in the film.”

The phrase "Yippee yi yo ki yay" is from the theme song of an extremely popular TV cartoon in the 1950s (Quick-draw McGraw). You have to be an old fart like me, or Bruce Willis, to get this!

Theme song:

Yippie ki yay is an exclamation of joy that was popularly used by US cowboys in the mid 19th century