Meet B. You could describe B as small, shivery, asthmatic, bespectacled. You could also describe him as religious, so he was almost perfect for good natured probing.
One day, we were gently interrogating him about his wanking regime; he replied that it was sinful, then became wincingly tight-lipped on the matter. Eventually, a larger child got whiff of the conversation, and boomed "what, don't you wank, B?"
He finally exploded; "No, I don't, and I wouldn't want to, even if I could!"
There was five seconds of perfect silence, while every child said Grace for the wonderful gift they had been given.