Functions as a Verb and Adjective.
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Function as an Adjective:

1- Used as an interrogative expressing inquiry about the identity, nature or value of Samwell's Wat Wat in the Butt song.

Function as a Verb:

1- To engage in coitus with- sometimes used interjectionally with an object(as a personal or reflexive pronoun) to express anger, contempt or disgust.
2- To question what a person is up to.
3- Reference to are you ready to sing along to "WAT WAT IN THE BUTT"
4- Expression used when frustrated or Bored.
5- Usually Vulgar: the act of carrying out the words of "WAT WAT IN THE BUTT"