Common idiom used primarily in the United States (date unknown). Started by a brilliant scientist in leu of "Just kidding" or "Just pulling your leg".
(transitive) to tease or deceive for fun
(intransitive) to speak or speak deceptively for fun
(transitive) to tease or deceive for fun
(intransitive) to speak or speak deceptively for fun
by feistyfaz February 21, 2015