Ratjacket is a reputation or 'jacket' for snitching. Once acquired, a ratjacket is typically permanent. In the office and other environments where people become well-known to each other, the ratjacket is a form of social leprosy and can lead to ostracization and worse.
Emma noticed a chilly social thermostat at the office. To her horror, Emma realized she had a ratjacket after singing to management about Jenny and Heather's time-card collusion.
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...