I recently passed my full motorcycle licence. It's something I've wanted to do for a long time but, only recently, actually decided to do something about it.
You work in a bar, pouring pints for the locals. One of your regulars comes in; he's looking pretty grumpy today. "Whiskey" he snaps. You put down a glass and pour. You finish pouring and he necks back the drink. "Again", he snaps. Again, you pour and as soon as you finish he necks it. This repeats two or three more times before the grumpy man slams down the money for his tab and leaves. Congratulations, you have just taken part in a "Producer/Consumer" exchange.