Milk Bottle Locking Cap "Milkey"

Picture the scene... you arrive at work and, while your PC is booting up, decide to make yourself a nice cup of tea. So you wander to the kitchen, and open the fridge, only to discover that someone has used all your milk again - oh no! With a look of despondency, you return to your office, and resolve to find a solution to this problem...

This is a locking milk bottle cap, which requires a removable "key" to be able to open. The idea is that the cap rotates freely without the key, making it d