My girlfriend is a real treasure. I won't tell you where she's buried though.
Does she appreciate these murder jokes when they're at her expense?
Well, I happen to love her buried treasure.
I know your joke really doesn't mean harm, but be careful who you say it around. Some people would think you're minimizing the violence partners experience in relationships.
It's a joke, I'm only trying to show my love to her.
I know this is all in fun, and I can tell that you really do care about your girlfriend. Even if she doesn't mind being the subject of these jokes, however, there are many people who would be upset by a joke. Perhaps they lost a loved one, or know someone who suffered in a violent relationship.