know (one's) beans

To be knowledgable about and/or very familiar with something. I had no idea you were such a good piano player—you really know your beans!

Name	Pronounced	Usage
Margarita	mahr-gah-REE-tah (Spanish, Russian)	Spanish, Russian, Bulgarian, Lithuanian, Late Roman
Golden	['gəuldən]
Traherne	-	Welsh
Sara	['sa:rə]
Philippine	fee-lee-PEEN	French
Dyer	['daiə]