Maternal insult

A maternal insult (also referred to as a "yo mama" joke) is a reference to a person's mother. This is through the use of phrases such as "your mother" or other variations, often used to insult the target by way of their mother. "Your mother" can be combined with most types of insults, although suggestions of promiscuity are common. One of the purposes of these insults is to incite violence. Slang variants such as "yo mama", "yo momma", "ur mom", "yer ma", "ya mum", "your mum", "ya mudda" or "your mom" are sometimes used, depending on the local dialect. 
Historic examples.
When Joram saw Jehu, he said, "Is it peace, Jehu?"&lt;br&gt;
And he answered, "What peace, so long as the harlotries of your mother Jezebel and her witchcrafts are so many?"
"Painter": "Y'are a dog."&lt;br&gt;
"Apemantus": "Thy mother's of my generation. What's she, if I be a dog?"
" “...of your mother is by the one who has intercourse with her. What/who is it?&lt;br&gt;
(No answer)”
While it cannot be completely deciphered, it is clear some comment is being made about somebody's mother.