If Jeb ever adds bananas to the jungle biomes, then there will be the inevitable desire to take that leftover banana peel and place it on the ground for someone or something to slip and fall on.
So my idea is this:
After you eat the banana, you will still have the peel left over. It could be a new brewing ingredient, or you could right click a block while holding it and place it on the ground. Anything that steps on it (even you) will slip and fall on their rump, and be immobile for a couple of seconds while they get back up.
Let me take it one step further and say, instead of imobilization, how about the player walks like they are on ice for about two to three blocks. That way, it wouldn't be as annoying to players, but the effect of paralyzation could be added when used on mobs. Maybe a little spinning animation while they are paralyzed. The animation would be pretty subtle, as to keep the Minecraft look.
Will be used for a lot of griefing in multiplayer (note: griefing means destroying people's fun, not only structures), so I don't think this is good.
So people who would have fun with this shouldn't get it because other people might be dicks? Seems to be that sort of logic is just another form of destroying people's fun. This is why admins and mods exist on servers: They deal with griefers.