Originally Posted by kidistight
He was already an ANBU member, I think that he can come back and be a member whenever he wants, he is already probably the best jounin in the village. Regarding how to become an ANBU member I think that you just have to be an above average ninja with exceptional talent and abilities.
Actually, I truthfully think Gai is equal to, if not a "better" ninja than Kakashi. Remember when Gai held his own against Itachi, where as Kakashi could not? That's only one instance, but nonetheless. A ninja is defined by how he handles situations, and Kakashi has a history for locking up against powerful opponents. (He got choked up when talking to Orochimaru during the Chuunin Exam, and he got scared when facing Itachi.)
Also, other than Gai. Remember that "Sennin" is just a title. Tsunade and Jiraiya are still Jounins. And I believe they are better ninja's than Kakashi.