n. A character in a science fiction show, who dies soon in the episode. This character often acts nonchalant or sometimes even cowardly. Often their name is only mentioned in passing, or are given no name at all.
Taken from characters in Star Trek who wore red shirt/jackety things.
Random guy: What could possibly go wrong?
Other character: Ooooh, he's gonna be a red jacket...
"Hey Mom! I lost my Red Jacket today!" - you
"Well i guess I'll have to buy you a new one then..." - mom
"I don't think that's possible ;]" - you