Shiki is a discord person who has played with multiple girls and has gotten nudes and then broke their hearts aka breaking up with them. But they go through "shiki syndrome" and they keep liking him and simping for him while acting like they hate him. After "shiki syndrome" they auctually start hating him. shiki'd is a inside joke word for "That girls gonna get played"
Jessica: I like you
Shiki: I like you too...lol..
Person: They girls gonna get shiki'd
A person who has had multiple girls and a person is now hitting on the said person
Person: Hey jessica "I like you"
Jessica: I like you too
Person 2: She's gonna be shiki'd