JKIS
A more formal and apologetic way to say, "Just kidding". If you were for say making a joking that somewhat angered or offended a loved one or someone you know, you could say, JKIS, if you know that JK would continue to have to enraged, which they may get violent.
For example, "JKIS, don't worry!" You should make sure to say something like "don't worry!" Cause you want them to know it's okay, and you meant no offensive in your act/joke/prank/etc.