Attack on Titan

Your nickname for him

Eren: You often call him a Dork because of the cheesy things he does and the way he acts around you sometimes.

Armin: When you are alone or just talking to each other you call him Cutie because he is just too cute. But otherwise you call him Blondie, it annoyed him at first but now he likes it.

Levi: You call him Captain just to irratate him, but you also call him Babe because you don't think he needs a silly pet name.