Next time the new guy asks you to do the busboy job, tell him  "Thats a good idea. Since I'm already doing the dishes though, why don't [u]you[/u] do the bussing before you get too wet this time and next time I come to work after your shift, I'll bus the dishes so you don't have to leave your station." This does not demean his thoughts but still maintains you as the veteran to the work scene. 

I've bussed tables and washed dishes and even been a waiter when one of the others had to leave early. I know how much the stress gets to you, doubly so with stupid coworkers.