Self-loathing program/function
05AB1E, 20 bytes
&quot;34çìD«QiF&quot;34çìD«QiF

Outputs the input if it's not equal to the program. If it is equal, it will output the error:

** (RuntimeError) Could not convert &quot;34çìD«QiF&quot;34çìD«QiF to integer.

Try it online.
Explanation:
It's based on this base quine: &quot;34çìD«&quot;34çìD«.

&quot;34çìD«QiF&quot;           # Push string &quot;34çìD«QiF&quot;
           34ç        # Push 34, converted to a character: '&quot;'
              ì       # Prepend it to the string: '&quot;34çìDJQiF'
               D«     # Append a copy of itself: '&quot;34çìDJQiF&quot;34çìDJQiF'
                 Qi   # If it's equal to the (implicit) input-string:
                   F  #  Start a loop, using the (implicit) input-string as argument,
                      #  resulting in the error
                      # (implicit else: use the implicit input as implicit output)