When is it appropriate for couples to swear at each other?

sometimes I catch my boy friends swearing under their breath about their girlfriends (not exactly playfully) and often call their girlfriends stupid when they are there.When is it appropriate for couples to swear at each other?
It is never appropriate to swear at or call them names. It's immature, disrespectful and shows a lack of respect. This kind of behaviour should never be tolerated. This goes for guys and girls as well.When is it appropriate for couples to swear at each other?
Never, otherwise there is no respect boundaries
what?
my ex bf used to call me a *****