Zach is about to shoot a venomous glare at the stock-boy, but figures that won't help matters just now.

He turns to Superman, speaking loudly enough for the correction to be heard by the stock-boy as well. "Zatanna Zatara is my cousin, actually, not my aunt."

Okay, the half a tux comment pushes his good nature, and he gives the boy a scowl, muttering under his breath. "Bad form..."