I'm going to tell my boss while he's on a work trip that I do not want to train his new employee
Why don't you want to train this employee?
I don't feel like doing favors for the boss.
Instead of adopting the perspective of doing something for someone, you can see this as investing in your professional network. If you show your coworker the ropes and do it well, you may be able to count on them for help and connections in the future.
I don't need that shit.
You may think you don't need it now, but in the future it can help you out. You never know what can befall you later on.