Green’s Dictionary of Slang

j.k. phr.

[abbr.]

just kidding.

[US]J.L. Gwaltney Drylongso 157: I have a lot of J.K. and mother wit on this thing.
[US]Eble Campus Sl. Nov. 4: j.k. – just kidding: Man you look awful tonight. JK! From an abbreviation used in internet chat.
[US]C. Eble (ed.) UNC-CH Campus Sl. 2011.
[US]C. Eble (ed.) UNC-CH Campus Sl. Spring 2016.