In this case, you can use either one:
1a. No one calls us names except for us.
1b. No one calls us names except us.
In this example "us" is the list of exceptions to the set of all people ("everyone"). When you have a discrete set like this, you can use either one with the same meaning.
But sometimes you don't have a discrete set. For example:
2a. It was a pleasant day, except for the weather.
2b. *It was a pleasant day, except the weather.
"A pleasant day" isn't a discrete set of things to which "the weather" is an exception. As a result, you need except for.
You also use except for at the beginning of a sentence:
3a. Except for me, everyone got to eat cake.
3b. *Except me, everyone got to eat cake.
But you typically use except before a preposition phrase:
4a. ?She likes to go for walks except for on rainy days.
4b. She likes to go for walks except on rainy days.
(People do say things like example 4a, but it's a lot less common.)
You don't like to see others suffering, except if they're suffering for you.
except if here is the same as unless.
except can otherwise only be followed by nouns:
You don't like fruit except for bananas.
You don't like driving except if [unless] you are the driver.
except + [if clause]=unless
You would have liked the movie except if it had been really bad.
In more formal writing, it's better to use unless, in everyday utterances except if is fine.
Best Answer
In my experience, when we exclude technical books on software and programming, and focus instead on other kinds of prose, it is unusual for a sentence to start with Except if. Most often, an except if-clause is added on as a qualifier after the matrix clause rather than used as an opening condition. On the other hand, unless-clauses appear before and after the matrix clause.