Ding is often used as a replacement for saying "That's what she said." It originated from a person ringing a bell whenever such a statement was necessary.

Anatidaephobia is defined as a pervasive, irrational fear that one is being watched by a duck. The anatidaephobic individual fears that no matter where they are or what they are doing, a duck watches.

Anatidaephobia is derived from the Greek word "anatidae", meaning ducks, geese or swans and "phobos" meaning fear.

in mmorpgs, esp. WoW, *ding* is used to notify others in your party/guild/etc. that you have just leveled up