1) Write him/her back; used when someone writes/e-mails to someone he or she is interested in; then when that special someone reports this to his/her friends, the friends say, "WHB!"
2) Win him/her back; used when someone breaks up w/ another individual (or vice versa), and that someone's friends are trying to encourage that someone's friends to revive the relationship.
1) email@example.com: "Oh like this guy wrote me, I think he like is totally hot and he definitely digs me! What should I do?!"
2) firstname.lastname@example.org: "I don't know, like, he's a pain in the butt but I still like him, it's only been, like, a week and stuff, I don't know what to do!"