"unf" means: Inarticulate grunt of desire issued upon sighting someone sexually attractive, or made in response to a spasm of pleasure during sexual inte.... The term has a sexual reference, so parents may want to know the context in which a child uses or hears it. In most cases it is part of normal teenage curiosity rather than a concrete worry. A short, non-judgemental conversation about consent, respect and online safety is usually the best response. Look at the wider pattern of behaviour, not the one word.