Optimism is the psychological behavior of believing a specific endeavor will have a positive or favorable outcome. Alternatively, optimism is also the philosophy that this world out of all possible ones is the one most worth living.
Personality
Of course, optimism will act... optimistic. It would seem he feels no other emotion besides happiness and is willing to help others out with their problems. It would make constant attempts to cheer up 
Nihilism, but would fail each time.
Relationships
Friends
Anti-Nihilism - My best friend!
Theocracies - I'm sure god loves you all and will recognize all of you.
Marxism - Communism can be achieved if you can just keep trying.
Alter-Globalism - Another world is possible!
Feminism - You can do it!
Apoliticism - You make the best brisket!
Frenemies
Nihilism - Come on, cheer up a bit! I do like your optimistic variant though.
Enemies
- Enemies? Why would I want those?
Pessimism - My opposite!
