Never kid about divorce, planting those seeds is where quitting starts.

If you were to employ someone, kidding with them about firing them may seem funny to you but could be incredible cruel to them.  If done enough with your partner, the Illusionary Truth Effect may come into play and your partner, deep down, may think you are serious about calling it quits.  There are plenty of other things to joke about, don’t joke about ending a relationship that is meant to stand the test of time unless you are no longer interested in that.