I regularly say things to my Girlfriend that could be considered by a outside party as very offensive. However, we do it as a joke because we both think the same thing "My God, why do you put up with me?"
I assure you. It's always done with a grin if joking.
Some examples?
Her- Why do you put up with me?
Me- Cause you're a cheap whore and a easy s**g
Her- Oh really? That's always nice to know Jack.
H-I'm going to the loo alright?
M-No it is not alright! If you leave right now I'm leaving you and I'm gonna sleep with your best friend.
H-That's exactly what I was thinking too. I'm already slept with your best friend too. Perhaps we can swap stories?