Adjective/Verb. Used to describe situations which are both amusing and acceptable (1). Also frequently used in the negative form to express shock or dismay (2). Can also be used to describe any trek or adventure undertaken whilst under the influence of cannabis (3).
(1) 1: Look, I made a bong out of a pepper!
2: Dude, that's totally guaning.
(2) 1: I raped your mother.
2: Oh what? That's not guaning.
(3) 1: Wanna come over and play Tekken?
2: Can't, I'm guaning on out.