Dog watching-What did I agree to?

Question
Hello, my name is Lucy and I thought I was doing a good deed by watching a family member's Jack Russell Terrier and their smaller terrier. As it turns out, the "JRT" is severely aggressive and poorly trained. When I came over to learn the whereabouts of their food, leashes, etc. he immediately jumped all over my boyfriend and I, then proceeded to growl and snarl. They put him on a leash to restrain him and he struggled against it choking hard, to which they responded by TREATING HIM and then ultimately muzzling him, but not before he got a hold of my closed fist and bit me. They did not discipline him for biting me, instead they sat there apologizing and making excuses for him.

Today, we went over for the first time without the owners in the house. The first trip was fine excluding a few barks at the start and some terrible leash habits which we were easily able to handle. However, the second time after their successful walk, their Jack Russell jumped on the chair with me (I have no idea WHY they permit him to be on the furniture) and sat still for a few seconds before psychotically trying to rip off my face. I unceremoniously pushed him off the chair and said "NO!" to which he responded by facing me, snarling and barking loudly. The other dog urinated on itself out of fear.

As if that wasn't enough, I called the owners and they said, and I quote, "Give him a piece of cheese!" I refused, grabbed the clicker, made him sit still until he was calm enough for me to turn my back to leave.

He's not my dog, so I can't expect a discipline routine to stick. He is also insensitive to most verbal commands unless I am where the treats are. I have only treated him twice- once after a good walk and once for sitting calmly when I used the clicker. Still, he was terrible and treatless tonight and I'm dreading seeing him in the morning.

What can I do to make the next few days with him bearable?

Answer
What a terrible shame that your relatives are turning this dog into such a horrible creature! What he needs is long-term obedience training with daily lessons and religious enforcement by all in the family of "Nothing in Life is Free". http://k9deb.com/nilif.htm

I think you are on the right track by only rewarding his good behavior, and I would try to ignore the bad... at least do not react unless he is attempting to bite. I would take total control of his resources... give him his food one piece at a time... all of it, just as you would do when "charging the clicker" when teaching a dog what clicker is all about. I would also up the value of his treats by making it something really irresistable... cheese is usually good, or chicken.

When the relatives return, I would remind them that if this dog bites someone, they could lose their household insurance. They need to learn how to train him correctly.