caai/zaai si -nonsense? full of it?

Hi all,

I overheard an expression of zaai/caai (which I think may be 柴屎) based on tones - with the context of someone who is full of it (bull****), someone always acting big. I couldn't find the character for zaai/caai but it was one of the lower sounding Cantonese tones (I think it was around tone 4. Has anyone heard this expression before? Any input would be greatly appreciated.

Thank you!
~Lily