The term came about after a reference was made to the "TWiT Army" and speculation began as to what fans of NSFW might be called. The term is a reference to the infamous dolphin being used as a masturbation tool that appeared in a Tinychat window during the Ask the Internet episode of NSFW.
Origin of the Phrase
The discussion starts at 1 hour 29 minutes and Leo utters the phrase at the 1:29:58 mark.
Disuse of Phrase
The phrase was used less and less often towards the end of 2010 as the term "Chatrealm" came to prominence. This is partly due to the fact that Brian and Justin can't actually say "fuckers" on NSFW, but would not get censored for saying "Chatrealm".
Later, Diamond Club became another common term for the biggest fans of NSFW.