He didn't give himself the title, he inherited it.
That's really quite irrelevant. Whether he personally attributes it to himself, or whether his followers attribute it to him by virtue of his position within that cult, the fact remains that he is not worthy of such a title. Christ alone is Holy and He imparts that Holiness to His Church, hence the worthiness of Saints and Heirarchs of the Church bearing such a title.
You still didnt say whether you call the Pope the Pope.
Well putting aside the fact that the RC Church stole the title Pope from the Alexandrians, I woul probably say "RC Pope", which is alot more objective. Tell me, would you attribute the title "His Holiness" to the Pope? Don't all the Apostolic Churches, whether they be RC, OO, or EO qualify their Patriarchs/Popes with "His Holiness" and their Bishops with "His Grace" or "His Eminence"?
Would you call our Coptic Pope "His Holiness Pope Shenouda III"? No, and I wouldn't really expect you to. Yet somehow Mr. Lama earns that title?
And you didn't answer my question as to whether you would address Muhammed as "The Prophet Muhammed".