“Do not curse the deaf.”
~ Leviticus 19:14

Words spoken from an angry heart with ill intent hurt.

But if the deaf cannot hear, surely they won’t feel any pain?

They won’t but you will. Although the deaf won’t even know about it, there’s still a negative impact on the one who said it, because they said it.

Cursing is like punching a wall in a fit of anger. Although you won’t break your tongue as you would your hand, you nonetheless defile yourself by simply losing control.