A type of "prefanity" (predicted profanity) invented by Gabe and Tycho, the writers of Penny Arcade, who foresee its use in the future on XboxLive. The phrase's meaning can only be speculated upon, but it almost certainly will be derogatory.

the whale tail is the shape formed when a g-string rides up high over a womans trousers

Originated by the Penny Arcade strip "Prefanity", "Strawberry Smurf" is some perverse term involving arbitrary sexual acts, necrophilia, and gnomes. This can include any form of Gnome, whether it be from Warcraft, D&D, or just an exceptionally short person in real life.