A reply to a horrible, lame, or downright pointless joke. You also finish it with an epic "line face" (definition elsewhere)

A response to something that is really unfunny.

Doggy sound which can be substituted to woof, bowow, etc.

a word used when someone makes a corney joke, bad pun, etc.

A doglike sound used to ward off haters or opponents...

This word was commonly used in the British magazine PC Gamer and later spread from their official forums to several IRC channels and other forums.

When someone would make a joke that is funny as well as slighting shocking (although this last part has become optional) people would reply with a simple "Arf!"

Term meaning a person of African decent who cannot swim or swim well. Derived from the acronym A.R.F. which stands for African Rock Fish. Used by lifeguards or ride attendants in the U.S. northeast who generally work at the jersey shore or water parks near large urban areas.