Well, it could be about their playful banter in the werewolf pack. Maybe they tease each other about their hunting skills or who can run faster in wolf form.
Perhaps the tease story is centered around their different approaches to dealing with the presence of vampires. Jacob might tease Leah for being overly cautious, while Leah could poke fun at Jacob for being too eager to confront the vampires at times. Their teasing could be a way of coping with the constant threat that the vampires pose to their pack and territory, and also a way to relieve the stress that comes with protecting their loved ones and their way of life.