This is bad news isn't it? Perhaps the weird one doesn't mean to be intentionally unpleasant, but you DO need to take your friend to one side and point out how upsetting this sort of behaviour is, and how distressing it was for the child. Please keep an eye on things if you can, and if anything further happens, make it clear that you object, and that you'll take things further if it doesn't stop. You might even lose your friend because of it, but the child's welfare is more important.