Dealing With a Bratty Wife

Anyone have any advice of how to deal with a bratty (or bitchy, or whatever you want to call it) wife? It isn't so much that she's being a brat to me (she is, somewhat). It is that she's been bratty towards others, needlessly antagonizing them when they don't do what she wants, when she wants, how she wants. Example... she wanted her brother to babysit. He declined. She started ripping into him about what a loser she thinks he is, point out that she went to college, graduated, got her career going, and doesn't abuse alcohol or pot or illegal drugs (she just loads up on coffee, candy/sugar, and has multiple prescription pills she pops), while he is unemployed, has no college education, and has abused substances... but we still trust him to watch our kids for short amounts of time.

I gently asked if her treatment of her brother was going to make it more or less likely he will want to babysit for us in the future.

I'd like to apologize to her brother and others she's been acting this way towards lately, but I have a strong belief in marital unity and not going behind your spouse's back, and all of that. Besides, she should be the one apologizing, right? Do I encourage her to do so?

My wife has been especially stressed out because of a series of things, but currently it is about an impending surgery. But... dealing with stressful things is part of life and no excuse to antagonize people.

Any tips or suggestions about what to say/do towards her or the people she's antagonized?

Please don't say sex. I can't sleep with her brother. But seriously, sex doesn't relax her or put her in a better mood. It does relax me and put me in a better mood, though. And yes, I do realize I could have avoided dealing with a bratty wife by marrying someone else or not marrying at all. But here we are.