Use your imagination and creativity to plan a birthday party for an adult friend or relative that they won't forget. Start with a fun theme idea, then build on the theme with a delicious menu, festive decorations, and engaging entertainment. Want to find a party theme that will allow guests to have fun and use their imaginations? Host a hat party! Hat parties are a simple but quirky way to create a theme for a birthday, housewarming, or other fun occasion. Cover your head with a fantastic Adult Birthday hat from Zazzle! Shop for embroidered hats, trucker hats, & visors.