“Would it be unethical or offensive to get a bunch of fake teeth, paint it to resemble fake gold, and mail it off to “Cash 4 Gold” or other places similar to it and include a card that says “Do you guys take Nazi gold?” to get back at them for all their advertisements?”
(Yes.)
Ethics Alarms 
It would be an interesting case study in just how idiotically gullible some people can be.