The Brief: JK stands for "just kidding."

DEEP DIVE
JK is an acronym for “just kidding.” It is used to negate a previous statement or to retroactively indicate sarcasm. Common usages include pairing with LOL (as in “lol jk”) and using multiple JK’s (as in “jkjkjk”).
i donβt think i can post my new vid today itβs prob gonna go up tommorowπ
jk pranked uππππ posting in like an hour or two π€ π€ ππππ
— Antonio Garza (@antoniiogarza21) January 29, 2019
If you want to stay warm, @matt_mccutcheon is being generous and giving away some of his clothes. Lol jk pic.twitter.com/zhEVX4zEcz
— Frank Young (@FY3TV) January 29, 2019
Convinced Iβm prego because I ate my entire plate and salad from Olive Garden when I NEVER do, oh my lanta peroooo JKJKJK Iβm not prego
— Alejandra (@nandiiale) January 29, 2019