I made these cute "panty" cookies for a bridal shower and they were a hit. A friend and I decorated around 2 dozen cookies to share with our girlfriends. We used a heart shaped cookie cutter to make the bride's bum. Then we whipped up some royal icing, to create the panty outline. Here is a great tutorial with how to frost with royal icing properly.
To decorate, choose a few colors that coordinate with the theme of your party. Add some royal icing in a small bowl and add a few drops of food coloring, I like Wilton's, and mix together. Place the colored icing into piping bags. You can easily use zip lock baggies to frost, but I use piping bags so that I can use different decorating tips. While the icing is still wet, sprinkle a few colored jimmies to add some sparkle and embellishments.