While watching Candyman the other night, I was struck by one of the character's use of the exclamation "psych!" (Also spelled "sike!" by elementary school kids who didn't know that Greek prefix. We couldn't have seen it in print since it was only spoken.)
It not only means that what the speaker had said before was a lie, or that a connotation that the listener inferred was wrong, but that the speaker led the hearer to that false belief, and in a playful prankster way. It's roughly the same as "I had you going," "fooled you," and so on, except better because it was concise and commented on how the speaker used cunning or toyed with the listener psychologically.
I recall this word spreading sometime in my later elementary school years, late '80s or early '90s. Candyman was released in 1992. Then suddenly it vanished. "Not!" and "as if!" were not up to the job. They both meant that what the speaker had said or implied was a lie, but the context was not one of playing a fun practical joke -- it was to make a sarcastic and haughty dismissal. "Sure Mom, I'd love to babysit my younger brothers on Saturday night -- not! [as if!]"
You could also have used "psych!" in that sarcastic way, but it was a lot more versatile, allowing the prankster usage too. "Not!" and "as if!" couldn't be used in that playful practical joke way, though -- only in the contemptuous way.
During my many years of tutoring during the 2000s, I never heard the Millennials (whether children or high schoolers) using another word that could replace "psych!" Either it just went out of fashion or young people were far less likely to be in a playful prankster mindset after the 1992 peak of the violence level, paralleling the wider decline in wildness among young people.
Whatever the reason, it's about time for a new "psych!"