It's likely a made-up word or a playful mispronunciation of something else.
Here's why you might be thinking of it:
* "Shenanigans" is a common word meaning silly or mischievous behavior. People might jokingly use "Shananagator" as a humorous way to describe someone or something involved in shenanigans.
* "Shananigans" can also be used as a noun, referring to the mischief itself. Someone might say, "That was quite a shananigan" or "That's a real shananiganator."
Ultimately, the meaning of "Shananagator" depends entirely on the context in which it's used. If you heard it somewhere, try asking the person who said it to clarify what they meant!