Tell him Barney doesn't exist
Remind him he has the least fangirls
Ask him how he feels as always being the youngest.
Stick a Hug Me sign on his back.
Steal his teddy bear; tell him to hug himself.
Tell him he has grizzly stuck inbetween his teeth.
one of Rosalie's admirerers that she has a crush on him, and get him to surprise kiss her... right infront of Emmett.
Ask him why none of his powers have intensified.When he tells you it's his strength, tell him everyone has that.
When he tries to argue, jump up on a chair and start screaming, "Emmett's a human! Emmett's a human!"
Make the grizzly's extinct.
Tell him a real boyfriend would fix his girlfriend's car, and not the other way around.