I was standing under the shower, trying (in vain) to drown out the sound of the screaming children around me, when one of them flung my shower curtain open to stare inside. What part of the closed shower curtain and running shower caused her to think my shower stall might be unoccupied, I don't know.
Six months ago, I think I would've cowered a bit. Instead, I stared back at her, soapy scrubbie in one hand and bottle of conditioner in the other, and said, "Obviously, this one's taken."
Embarrassed, she tiptoed back out of the shower stall and closed the curtain behind her, then whispered an apology.