Ah the age old question of whether to swap seats. As others have already said, I would only swap for an equal or better seat, never for lesser. The only exception would be is if the seat I would swap to was worse but there was a really hot woman in the seat next to it. I may go ahead and take that.
A couple funny situations in my past:
1) A few years ago I was in First Class. A young teenage girls comes up and asks me if I'd be willing to swap for her economy seat. Her reasoning as she put it was: "I've always wanted to experience first class but have never had that opportunity. Would you make my dream come true?"
2) One year I was in an aisle seat. Woman on my right tells me that her husband is sitting on my left (middle seat) and if I would be willing to swap with him so they could talk to each other. I had to applaud her bravado to ask such a stupid request. Of course my reply was I'll trade you my aisle for your aisle and you can sit to him.