The New Meaning of Whore

Here's the situation:
I'm in the car, driving my 15-year-old home from school. There's nobody else in the car with us. He starts telling me about his day
(Someone once explained to me, after I had complained that my boys will only broach serious topics with me as I'm driving them somewhere and never while I'm sitting down comfortably at home, that boys will usually talk more, and open up more, in the car, where they know you cannot maintain eye contact with them. I largely think this is correct)
and he gets onto the subject of P.E.
Now P.E. is not my son's favorite class. He doesn't hate it, but he doesn't love it, either. His favorite class is actually Physics. Followed by Calculus.
Jock he is not.
But he has a nice group of friends in P.E., and they all just kind of hang out together and bear it collectively. They call themselves the "Nerd Herd," both in and out of P.E.
Son starts telling me about things they were discussing during P.E. time—words like "linux" and "steam" and "portal" and "pie graphs" and "Alpha" and "Beta" start flying out of his mouth and straight over my head—and then I realize he's started to talk about people.
"So Beta thought—"
"Wait, Beta is a person?"
"Yeah. We have names in the Nerd Herd. I'm Alpha, cause I'm Alpha Nerd. They decided."
(I am so not surprised.)
"Beta is second. When I'm out sick, he's the Alpha, but only when I'm not there."
"Okay....wow. What are some of the other people's names?"
"Well, we have Omega, and Fucker—"
"Wait, you have someone who's nickname is Fucker?"
"Yeah. He wanted it."
"Oh sheesh."
"If you don't like that, you're not going to like the others."
"Okay," I say, granting he's probably right. "But what about the girls? You do have girls in the group, don't you?"
"Yeah. Two."
"What are their names?"
"We call them the whores."

At this point, it was hard for me to drive, because my jaw was jamming the steering wheel.
"Son," I say, "that is NOT OKAY. Why would you do that? Why would you call these two girls whores? Do you understand how hard it is in general for girls to be nerds? How everything they do ends up being tied up somehow to their sexuality? How they're put down and insulted for daring to try to be included in circles of gamers and nerds?"
"Okay. Jeez, mom."
"No, it is not okay. It's very wrong for you guys to call them whores, just for being members of your group. What the hell were you thinking?"
"We were thinking it's funny."
"Well it's not. At all. You need to stop."
"It's supposed to be derogatory towards us, mom. Towards the guys."
"How—how is it derogatory towards the guys?"
"Because the joke is that no girls would be willing to be in our group unless we paid them."

I didn't have a clue what to say. I'm not exaggerating here: all possible answers were just wind-swept out of my head. Because when I looked at it from his point of view...yes, they were insulting themselves, not these girls, and certainly not women in general.
But it still didn't sit well with me.
Son then went on to tell me that the girls know about the name (it's not something the boys call them behind their backs), that they agree it's funny, and that they laugh about it, too.
Does this make it okay?
Can it ever be okay to call a women whores?

But then, maybe I'm whore shaming now? Certainly a woman has the right to label herself whatever she wants, and not have to get flak for it. The word "whore" doesn't have to be derogatory unless we designate it as an insult.
It can be a fact, not an epithet.
But for a group of boys to label girls "whores," even if it's to put down themselves, even if they don't mean it as an insult to the girls in question...it bothers me.
I'm just not sure I can articulate why.