There are so many acronyms, slangs online, getting to know all of them be extremely difficult, but knowing the popular ones might savage the situation. One of those popular acronyms is JK, which simply means Just Kidding.
JK is a very common slang on social media, people use it when chatting with their friends. 'Just kidding' means you are not serious what whatever you said that probably did not go well with the recipient. You know, some people are good at teasing or telling some craps about you even in your face, so to let you know that they don't mean what they are saying they will use JK which means 'I'm just kidding'.
People use JK at the end of a sentence, so that they would have achieved what they wanted before you realize they were just kidding. For example, someone might decide to say, ''Why do you look so unkempt this morning......Jk''. The person includes JK to let you know he's not serious about the comment.