In our group, where three of my friends and I play, one of my friends—let's call him John—always plays characters like himself, and always the same class: a swordfighter with psychic abilities.
John has been playing himself for 2 years, through 4 parties.
We have tried to convince him to change the class, to have a different atmosphere around his character. He said, that this is the only class that interests him.
We tried to have some roleplay practice night, where the GM assigned some predefined roles for a quick roleplay game. In one of these games, he had to play a fat butcher with some predefined traits: gullible, stupid and strong. He upright couldn't play it, stating that he "thought of everything there is, but he is out of ideas". We tried to encourage him with some ideas, but he rather not played it.
We tried to be forward with him and told him, that he plays himself, bringing up situations where he reacted the same, the way he talks (trying to sound "deep" and concerning), that he is always plays polite (except when woman NPC is around). But he denies it...
It's like he only likes to focus on solving the quest, rather than playing the quest.
All of this wouldn't be a problem if his character would be fun, but it is not that case.
How can we help him accept that he plays himself, and help him be open about trying out other characters?
I feel like he didn't improve his roleplay while roleplaying for two years. How can I make him see that by trying things differently, he will improve?