* It's a misheard idiom: There might be a similar idiom you are thinking of, such as "you're not a piece of cake" which means something is not easy.
* It's a colloquial expression: The phrase might be used in a specific region or community, but is not widely recognized.
* It's a made-up phrase: Someone may have created it to express a specific meaning, but it doesn't have a widely understood definition.
To understand the intended meaning, it would be helpful to know:
* The context in which you heard it: Who said it? What were they talking about?
* The speaker's tone of voice and body language: Were they being serious or sarcastic?
Without more information, it's impossible to give you a definitive answer.