"Do you keep any coke in there ?"

"Yes, and heroin,moonshine and opium.."

Quite the 'inside' joke for the times! Even a daring one considering the negatives it could have unnecessarily caused with the average movie goer - even pot smokers were considered maniacs back in '62.
But, more to the point, if the boy went home and repeated this to his dad, think of the unwanted attention this could have brought down on Macklin/Perkins !