I accidently put a character on one of my watch list twice and can find no way to remove it. It would be nice if there was a simple way to do this.
It is a drag and drop interface. As you drag a character, a box will appear in the upper right that says "Drag characters here to remove them". Just drop the character on that to remove it from a group. Due to the way they are stored in the database, if they are both in the same group it will remove both by removing one. Just re-add it back afterwards.