It really should go without saying that you should never record someone without their knowledge, regardless of the location or circumstance. It doesn't matter if that person is in your home. No matter what, that person is going to feel violated and betrayed. (An obvious exception to this rule is if you or someone else is in a possibly dangerous or threatening situation.) So, yeah, if you're recording a guest in your home without their permission, don't be surprised if that person is upset when…