Facebook Reciprocity 

The act of clicking "like" or commenting on someone's facebook status when you otherwise wouldn't have, but you complete the act because that person has commented or "liked" many of your entries.

Guy: Did you really comment on that picture?
Other Guy: Kinda had to, he's been commenting on my status ever day. Facebook Reciprocity.

Facebook Reciprocity by P. Nathan Poothy January 11, 2011