Well if it's a regular user account with its own /home folder:
Then you could try logging on to an admin account, and using "userdel" from the command line.
Your best option may be to use the -r option to also remove the /home/guest home folder .. as in:
If it still won't budge .. try the -f option to force removal.
But as you say .. if it's working as you want .. why bother