There are countries that don't have extradition treaties with the US for anything, though many of them are places you might not want to live...
Wikipedia also has a list of countries that the United States doesn't have an extradition treaty with. https://en.wikipedia.org/wiki/Extradition_law_in_the_United_.... Most of those don't look like great options, but a few of them are quite nice!
Whether or not a country will assist at all in enforcing a civil judgment from a foreign jurisdiction is a matter to be explicitly spelled out in treaty agreements.
Your best bet for avoiding a civil judgment is probably to just be too difficult for a process server to find to serve you with the complaint and summons, or failing that, to make a special appearance to assert lack of jurisdiction before making your answer.
IANAL. While I'm not particularly inclined to offer helpful advice to those who would try to skip out on valid debts, I am even less inclined to allow the typical institutional lender or debt collector to go about their business as usual and win by default.
I had a friend who was born in the US, while his parents were on vacation, so he automatically got US citizenship even though he never lived there. And dealing with banks in his "real" home country was becoming more and more difficult. He was even forced to file taxes with the IRS, even though he literally lived in the US for the first 2 months of his life at most.
So, even if it's a one way ticket, just the fact that you have US citizenship can make daily life a little complicated .
He would have been granted whatever citizenship his mother had, by that country, since he lived there while growing up. Any rights or penalties associated with the US citizenship would only come into play if he actively sought them out, having first gone to a US embassy and explicitly obtained citizenship for himself. Generally the only reason to do that is if one intends to move to and live in the USA.
This is a very common problem for people who acquired US citizenship this way, I encourage you to use Google instead of calling people liars.
I had a teacher in High School who had stopped paying his UK student loan (he was in New Zealand), he had no plans on ever going back.