noun. A "jenkin" is a person who is always complaining, easliy annoyed, and usually a bitch. To be a jenkin you would have to be extremely condescending and never pay attention to anybody elses ideas because you think you have even better ones.
verb. To jenk or to be jenking, would be to insist that you are the best at everything and no one could ever be better.
"Dude, I'm tired of you always jenkin', just listen to what I have to say".