Sike

Spell-it-how-it-sounds version of "Psych."

"Sike" (or, more properly, "Psych") is a declaration that you just deliberately messed with someone's mind. Literally, "I fooled your brain."

"Psych" is a Greek root-word meaning "mind" - found in many other words, such as psychiatry, psychotic, psychic, psychedelic, etc., all of which relate to the mind. Note that the first syllable of all those words sounds like "sike."

The "Sike" spelling is most often used by people who have never read a book and are therefore only familiar with hearing the language spoken out loud rather than seeing it in written form.

Bill: I truly respect and value your opinion, man.
Ben: (hopefully) Really?
Bill: Sike!
Ben: (sobs)