This morning, I was musing about whether insults of the "your mother [insert obscene activity here]" variety would constitute slander. Slander is a verbal false statement made to someone other than the subject of the statement -- and by definition, "your mother [etc]" statements are made to someone other than the mother. And it would be quite a coincidence, in most cases, if they were anything but false. I wondered whether the fact that such statements were meant to insult, rather than to persuade -- that the content was understood by all concerned to be false -- would keep the statement from being slanderous.
A little homework reminded me that to be slanderous, the statement must be one that would harm the reputation of the subject. If it's not meant to be believed literally, and would not be believed, then no harm, no foul (except possibly the language used), no slander.