If you can be on an even keel - regular and well-balanced and not likely to change suddenly when interacting with your loved ones and friends, then you are maintaining equanimity. It is important that you be the same person when you are talking to your friend or your wife. So that occasional sense of humor should be the same towards both of them.
We sorrow when we face of our everyday sufferings and troubles. And we joy when we face the moments of pleasure and happiness. When we behave indifferently in front of such pleasure/joy or sufferings/troubles it is equanimity that we are cultivating. One who practices equanimity will not mourn when sufferings, troubles find that person. He will not get excited when pleasure, happiness find him. He/she will feel all with an indifferent mentality.
You can cultivate this quality by repeating to self (as a meditation)… May I not be joyful because of gain… May I not be sorrowful because of loss… May I not be joyful because of praise… May I not be sorrowful because of dishonor… May I not be happy because of fame… May I not be sorrowful because of disgrace… May I not be happy by bodily pleasure… May I not be sorrowful by bodily suffering… May I not be happy by mental pleasure… May I not be sorrowful by mental suffering… May I be peaceful…