I'd avoid this approach. You don't have to be moralizing. Be straightforward and say "Hey I'm not cool with that. I know you're just teasing but I'd rather you cut it out, okay?" if it bothers you and they're a friend. Clear communication, not being moralizing. If they're a known piece of shit, walk away and don't waste your breath and energy taking it to heart. They're projecting their own insecurity and immaturity if they continue making fun of your voice.