What did "psych" mean?

The file

You offered someone something, pulled it back, and said psych. That was the whole joke and it worked every time for a decade. The Simpsons, Home Alone and every sitcom kid kept it going.

It's spelled psych, from psychology, but nobody who said it would have spelled it that way. Sike is the common misspelling and half of Gen X will fight about it.

Sources: Wiktionary — Psych!