You should firmly but politely tell her that such behavior is inappropriate. For example, you could say, 'I'm not comfortable with you slapping my ass. Please respect my personal boundaries.'
Acknowledge the awkwardness directly. You could say something like, 'That was really an unexpected and awkward moment. Let's not let it happen again.' This way, you're being honest about how you feel and also setting boundaries. Then, try to shift the focus to other topics or activities to ease the tension.
Well, it's not ethical at all. Workplace relationships should be based on merit and professionalism. If your wife is doing this, it can damage the work environment. It might lead to resentment from coworkers who are working hard without using such inappropriate tactics. Also, it can give your boss a bad reputation for accepting such behavior.
Another appropriate topic could be the trips you've taken together. Recall the beautiful sceneries, the interesting people you met during the journey, and the special memories created. It helps to strengthen your bond and gives you something positive to look back on.
This is an extremely inappropriate and abnormal situation that involves non - consensual and abnormal sexual behavior, which is not acceptable in a healthy relationship.
One of the best times was when we went to an amusement park. We rode all the roller coasters, ate junk food, and took silly pictures. We laughed so much that day. It was a day full of joy and it made our relationship even stronger.