How do you deal with a "Your mom" insult?

Shit like ie 'Where were you?' 'Busy finishing with your mom/sister/girl/etc.' etc. It's stupid I know but it's a fact of life many guys just jab and shit test people around them with that and sometimes even friendly jousting devolves to that and I usually have no good response. While it's immature it's does exhibit dominance. The common response is to just stand there laughing/IDGAF or use agree and amplify ("Yea, I fucked her too and it was great") but in front of everyone that makes the guy just look too weak to stand up for women close to him with any skill. A&A and laughing work with attacks directly on you because it shows you can take a hit, but when the attack is aimed at your family/woman these work against you. What comeback or deflection if any do you use?