A guy could tell a woman he could count on one hand how many women he’s been with, the woman would either lie, or get pissed you were judging her as it’s unlikely she could say the same thing.
Sure, he could TELL her that, but would it be true?
Nothing good comes out of a body count discussion.
It should be avoided if at all possible.
If impossible to avoid humor is the best approach. “Do I need to pull out my calculus textbook for this discussion?”
Most importantly the guy should never let the woman know he thinks she is lying—and of course keep calm no matter what she says.
The goal is to get her off the topic as soon as possible.