Why Do People Ask for an Opinion They Don't Want?

This happens to me all the time. It just happened with me and my quasi-supervisor. Maybe it just makes her look good like she is requesting input from her "staff." Anyway, I sent my suggestion to her via email and suddenly I hear a sarcastic laugh and a "why in the heck would I want to do that?" She tried to tone it down, but the damage is done. I always have the luck of working for bitches. There's no other way to say it. Of course she thinks she can do no wrong...