A metaphorical list in which people who are in ill favor with a given individual are placed.

(n) a list of entities exhibiting general disfavorability, particularly as a result of transgression. Presumably these entities will not receive the normal benefits enjoyed by those not on the list.
(v) the act of placing someone on said list.

A shit list is a mental list of things or poeple that have annoyed you recently. usually completed in a mental top 10 of annoyances for the most recent times and used as a public display of annoyance without offending people directly.

The list of banned, blacklisted.

If you don't like a person they are in your shit list AKA Hit List

Something you get put on if you've managed to offend, hurt, humiliate, contradict, disagree, bad mouth, lie, or cheat someone.

A list of people who have broken a rule or a regulation, disrespected an authority figure, or otherwise screwed up. If there is a job that needs doing but nobody else wants to do (i.e. a "shit job"), it is first given to the people on the shit list as a form of unofficial punishment.

This definition comes from the military where enlisted personnel who had pissed off their sergeant were the first ones picked for latrine duty; hence, "shit list."