[bell]

Yep........level with the guy and tell him you are not going to work on his car, sorry but that's the way it is......refer him to the local pepboys or other chain shop in the area.
You don't owe him **** other than a push out the door.
And make sure you have a sign that reads you reserve the right to refuse work somewhere, then stand by it....
Good luck, don't hesitate to call the cops if he gets loud...