A Mr. X or Y or Z does it in public.
Another Mr. X or Y or Z thinks silently and reflects, “please don’t scratch there…in public; you see, Suh, you see Saar, it isn’t polite”
A Mr. X or Y or Z still goes on at it—the scratching.
Another Mr. X or Y or Z reflects its idiomatic sense: “ to scratch in public…or scratch the public, and another X or Y idiomatizes: it as a social blunder— a faux pas.