The act of checking your speed while snowboarding or skiing. Originating from an unknown snowboarder who became famous for checking his speed when he should really have just manned up and pointed downhill.
"I knuckled on that jump because I guertined right before takeoff."
Noun: A sexual act through which a girl starts giving oral sex to a blindfolded male sexual partner and in the middle of the intercourse, she switches place with a gay/bi man who keeps up suckin'. Then, she removes the blindfold out of the confused guy.
Can also be used as a transitive verb.
Noun: She gave Leonard the good old Guertin.
Verb: Let's Guertin him to the max!