1. Refer to him as kira whenever you are supposed to say light.
2. Write his name in a fake page that you put in his death note and watch him freak out.
3. Call him kira after he for fits ownership of the death note.
4. When he says I'm not kira just say a long sarcastic right
5. When he gets the death note back scream I told you so in his ear.
6. Take L's cake put it on lights plate then say "L light took your cake"
7. Hide his death note take a page from it and don't give it to him
8. Carve you are not a god on his bedroom wall and then blame ryuk
9. Tell him you know L mellow and nears real names and don't tell him
10. Give him an alias so when he tries to kill you say "haha you can't kill me
This is the end of part one I will do L or matsuda soon.
Btw I forgot to mention this in the beginning of this but not all of the jokes in this are mine.