The act of wishing someone a happy birthday by commenting on someone else's message.
Basically, when it's someone's birthday on Facebook, and you don't know the person in real life, but know them through someone, so you comment on the post of the person wishing the birthday girl/boy a happy birthday.
Can apply to Birthday Status'.
Person 1: Hmm.. I don't really know Sam.
Person 2: Then why is he on your friends list?
Person 1: Linda introduced me to him.
Person 2: Then just Wallpost Ride her message.