I'm not going to help a new dishwasher do his job
Why won't you help him?
I heard that my boss likes him a lot and I'm afraid he will get promoted first.
You don't have to help him if you don't want to. Just be nice about it though. Tell him you are busy with something else.
Screw him I'm going to intentionally sabotage his work.
Not helping is one thing, but sabotaging his work is the wrong choice. Someone will find out you are sabotaging him, and you will be fired. Just do your duties as normal.