People mainly use keys in messages for two reasons – either as an insult or as a joke. Without realizing anything it can be harmful, use it carelessly without feeling. Other people can use it to threaten or hurt someone. KYS means severe, and even though it is in a joke, it can deeply affect one’s feelings. If you see this phrase in a message, encourage positive interaction instead. Although it depends on the user how could use the word and which context, so be careful.