The long answer: Meh... If the watch is old, you don't like it anymore, and it brings back painful memories of your ex-girlfriend who gave you the watch for your birthday last year but then dumped you for some jerk with a job and a car and who didn't use her credit card to buy a new drum set when you totally thought she wouldn't mind, then maybe.
So if you were wondering what would happen to a watch if you microwave it but don't want to set your house on fire trying, here's a helpful youtube video that will show you what happens when you microwave a watch. The watch in this case is some sort of digital watch, though I'm not sure of the brand (Casio?).
Anyway, have a look and enjoy. Then get a replacement Casio for after.