Okay, so imagine you're playing with some friends and you have a bunch of toys to share. Now, let's say one of your friends is really rich and has a lot more toys than you and your other friends. They might not want to share their toys with everyone else because they don't want to lose them or they think they're better than everyone else.
Now, let's say that some other kid comes over to play and they don't have many toys at all. But instead of just playing with you and the other kids who don't have as many toys, they only want to play with the rich kid because they think they're cooler or better.
That would be like a "class traitor". It means that someone from a lower class is betraying their own background or group by supporting someone from a higher class who has more power or privilege. It's not fair because it leaves out and ignores the people who really need help or support.
In grown-up terms, being a "class traitor" means that someone from a working-class or low-income background supports or serves the interests of people from a higher economic class or even opposes the interests of their own class. It can be seen as a derogatory term because it implies that someone is betraying their values and privileges over others in order to gain personal or social benefits.