Salty Mum

Alright, listen up, buttercup. This joke is about OP claiming to have slept with the listener's mom, and then saying she was "salty." Now, "salty" can mean a few things, like being upset or bitter. But in this case, it's a crude way of saying the listener's mom has a certain...taste. So, basically, it's an insult disguised as a confession. And you, my friend, are now in on the joke. Congrats, I guess?