Stefan cares not for Ethan's feelings at this particular juncture. And he's not going to tell Elena he was making dog jokes either, because he has common sense, but that won't really stop him from saying them anyway. When warranted. And probably not to Ethan's face.

(You should not do them to Ethan's face at all, Stefan. You shouldn't be making them at all. Stefan doesn't really particularly care.)

"Assuming that there's room to swim. Or the water's even real. Or there's an overboard to actually go over." No one's tested what happens if something goes over the side that he knows of. Maybe they just get magically zapped into place. Maybe they just go back where they came from. Hard to say, really.