TL;DR Don't trust what a woman says when she's "just joking around. She'll come back and use that as evidence that she warned you about something horrible. Jokes are just another trickle truth.

Intro
Something I often tend to do with a friend of mine is take long walks and discuss women. He's a MRA, I'm RP. We know this about each other, accept it and just keep it between us. There's something liberating about walking up the hiking trail of a mountain while getting your rage about women off your chest.

Today was different. This MRA has found a girl. She's Asian, small, cute, etc. He's extoling her like a Snowflake. Then he stumbled across something she said. "She grabbed my dick after sex and said 'this is mine. If you cheat on me, I'll cut it off.' but she was only joking -" I cut him off at this point and made one of my own. "Do you remember in college we had lessons about absolute values?" He burst out laughing, so I continued, "You need to next her now. You're not in your head, she's not a snowflake and you're losing yourself in it."

The conversation began to trail off, but I wanted to come back to this point about absolute values and what I meant by it. Because it was an enlightening for me, just having said it and hearing it as it was voiced and I made the connection.

The Maths
For those who don't understand, an absolute value in maths is when you take a sum (say 12 - 99 = -87) and for the purposes of understanding you do it to literally just find the numerical difference between two values, regardless of direction. You strip out the +/- from the answer and arrive at the absolute number. So the absolute value of the equation above would look like this:

(12 - 99 = |87|)

You take away some of the meaning to find the difference between two numbers. And in applying this to women, tell the story of what she said back to yourself.

"She said that if cheated on her, she'd cut my dick off. But she was only joking." I separated the sentences here clarity's sake, because the next part is "|She said if I cheated on her, she'd cut my dick off.|"

Yes I'm repeating that part a lot, and I hope my friend comes here and reads this. He attached pointless fluff to it that wont matter if/when she pulls a Bobbit on him and I'm the one rushing his sorry ass to the hospital with his Tuchus in a little baggy on ice.

Lessons Learned
Whether she says it serious or jokingly, she said it, and that makes you amply warned when it comes to pass.

As an aside, don't bother offering advice for my friend. I already led the horse to water. Its up to him to drink.