There are number of online tools, allowing you to have fun with images. Photofunia will allow you to apply funny effects on your images with couple of clicks, with no need to know any basic of the image editing.
No downloads or registration is needed. Just upload your picture, select the desired effect from the list, and it is done. Now, you can simply download the resulting funny image to your Hard Drive. There are more than 50 very different effects to choose from. An additional use for the free service is making a nice striking avatar for your forums or social sites profiles.
Some samples of my own picture effects application:
Web Site access: http://www.photofunia.com/