Difference – ‘Except for Us’ vs ‘Except Us’

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.)