Have a funny fear factor party. Make the challenge be something that is gross or very funny. For example: eat a large scoop of spinich, a spoon full of tuna covered in chocolate, or sushi etc.
Have them make a smashed banana split shake. They have to smash a scoop of icecream, a banana, and a tiny balloon that is blown up and has chocolate syrup in it...with their bottoms only. Smash it, put it in a cup, put a straw in it and then stop the timer. Who ever does it the quickest wins. (Rain gear needed)