As an Englishman I never understood the word Yippee-ki-yay, as in 'Yippee-ki-yay, motherfucker'. As Quentin Tarantino so wistfully put it, "I thought it was just a coldblooded thing to say to a motherfucker before you popped a cap in his ass. But I saw some shit this mornin' made me think twice."
Or, more precisely, I saw two things that made me think once.
The first is the Singing Cowboy, Roy Rogers, performing the classic song I'm An Old Cow Hand. (I'm afraid there's an advertisement at the beginning but it's very short).
The second is the original scene from the original Die Hard movie, from which yippee-ki-yay emerged. YouTube only has the audio, but that, gentle motherfucking reader, is all you need. Hans Gruber and John McClane are chatting away to each other on their walkie-talkies.
The line was repeated in the following movies (2: good, 3: terrible, 4.0: don't you understand decimal bloody places?) but in those later attempts to use the same shit twice, the meaning is, tragically, lost.