My friend is legally a midget. We jokingly make fun of her for it, but she jokes about it, too. It's just unspoken that when my group of friends says something like that we're joking. It's our way of saying "hey, you're cool enough I wanna waste time and say something off-the-wall about you".
And then we kinda make fun of J.Sens because he's super tall and bulldozed me last year (and knocked 2 of my ribs out of place) so we act like we still haven't forgiven him when we really have. He knows it, too.