The noise the worlds most beautiful creature, Waluigi, makes.

An ancient greeting bestowed upon us by the all-seeing high priestess Ninomae Ina'nis, performed by smiling, and rising your eyebrows.
It has been proven to reset your sanity levels when hearing it from her on a live stream.

Studies about its meaning speculate the word is a contraption of "lloig wgah’n", meaning: be/reside in psyche, however this hasn't been confirmed yet.

Something our god Waluigi would say. He wants to be in smash.

The sound the Peanuts characters parents make. Substitution for talking.

Further to earlier explanations, within the British Army, also used in response to an answer to an obvious question. This is a question that you have set the other person up to answer. Can become quite frustrating as you become paranoid answering any question in case it is a Wah!

"Wah" or "wa" !? Meaning what. Used in Irish slang a lazy way of saying what?

An exclamation, indicating misfortune of another person. Might be used in the same way as "unlucky."