R.W.
Giving him fewer materials may help. Also those crayons boxes can be a pain. Try giving him a different container for the crayons --something small clumsy hands can manage.
You are not raising a brat. Four-year-olds can be grumpy. =)
Let him know that Mom cleans up Mom's mess, and He cleans up his mess (at least certain kinds of messes). Let him know that if he can't be responsible with his art stuff then he can't DO art. Teachers require students to clean up materials also --and all the kids have to do it, not just him. It is part of life, like brushing your teeth or taking a bath, and if he does it without complaining, it makes grownups very proud of him.