#dnr - when you don't want anyone to reply to your posts
#cba - when you can't be arsed to bother engaging in an argument
#pmic - when a post is made in confidence and you don't want anyone to be difficult about it
#pbc - when you want people to be considerate of you
#nsp - when you post something sad but don't want any sympathy, please
#cuo - when you only want users you're comfortable with to reply to your thread

the possibilities are endless