Change the Comment Shape:

Add a bit of interest to a worksheet, by changing the comment shape from a rectangle.
1. Right-click the cell which contains the comment.
2. Choose Edit Comment
3. Click on the border of the comment, to select it.
4. On the Drawing toolbar, click the Draw button
5. Choose Change AutoShape, and choose a category.
6. Click on a shape to select it.
7. When finished, click outside the comment.