How can I exclude users with an EL Expression using Page Composer

Summary:

I want to exclude users with an EL Expression using Page Composer

Content (required):

We have a requirement where a field must be mandatory for all users except for one.

We had found an expression to make is mandatory only for one user i.e., #{WCSecurityContext.currentUser[‘userName‘]}

How can we change this expression to make it mandatory for all users except for one.

Please suggest.

Version (include the version you are using, if applicable):

23B

Code Snippet (add any code snippets that support your topic, if applicable):

#{WCSecurityContext.currentUser[‘userName‘]}