if you have a radiator in the house touch the case and the copper pipe that leads to the radiator. but really in most modern houses theres no need to do it unless you have nylon clothing on or a nylon carpet. as both will produce static electricity... just touching the case whether its painted or not you will still earth you as long as the pc is plunged into the wall... more often than not paint will have metal flecks. which is enough to get rid of any residual current your carrying.
Is there any easy tests using home materials that I can do to see if I'm grounded after touching something? I do have carpets, but they're really flat and I don't think they conduct electricity that much considering I don't recall getting shocked very often.
touching the metal case will discharge static on you even if the case is painted. Think about times you have touched something and felt a shock..its usually a person or a painted metal object..(there arent many bare metal objects in a household setting) and yes you are worrying too much