Informal negative sanction

"An "unofficial", non-governmental punishment for violations of social norms. Informal negative sanctions usually are in the form of gossip, public ridicule, social ostracism, insults, or even threats of physical harm by other members of the community. See negative sanction and positive sanction". http://anthro.palomar.edu/tutorials/cglossary.htm

(this can be easily found on Facebook bullying)