It costs nothing to be kind and friendly with everyone. From the custodian on up, there are no unimportant jobs or unimportant people. You never know when you are going to need the kindness and support of others.
Sometimes it's easy for people on their way up the ladder to look down on those around them, but remember that all are important and it takes a team to do any job successfully, no one can do it alone. And remember someday, you may be the one on the way down.