Flagging users as spam and giving a reason for doing so
Why not use the Flag Note module. 


  Extends the Flag Module to allow users to enter a note when they flag
  a piece of content and eventually build a flag history.
  
  Usage examples:
  
  
  flag nodes or comments for abuse providing a descriptive reason
  flag users as friends leaving a hint
  
  
  It's possible to opt to keep old notes even when the content gets
  unflagged