I just saw a TV show where contestants pitch their inventions/ideas to a celebrity who decides whether they're a genius or not (it's called genius). It's like a funnier Dragon's Den.
One of the ideas was a new way of defining opposites. If you want to find the opposite of something, you find its function and then find something with the opposite function. A freezer, for example, keeps things frozen, so its opposite is something that warms things up: a cooker. A hammer puts nails into things, but it also takes nails out, so it's a prime opposite.
I'll post something along with a picture, and the next user posts a picture of its functional opposite and explains why (If you can't find a picture on the internet, draw one in paint/photoshop/whatever or just leave the picture out), then they post something else along with a picture so that the next user can find its opposite. If you can't think of anything for the second part, try http://www.orderedpixels.com/misc/rand_obj/ :)