Just another day

Just like any other.
Question: Is it wrong to give people decaf if you run out of regular coffee? I mean is it unethical? Do they ever know? I know better than to give regular to someone who wants decaf, but I'm not so sure it makes a difference the other way around.
Sometimes, when I work at night, I'll let the high-test brew run out so I can clean the pots, and I'll secretly serve decaf. At night, this is an ethically sound trick to pull, because drinking too much caffeine late at night isn't good for you, and will lead to jitters, headaches, insomnia, and lethargy the following day. So really, you're doing the customer a favor by not injecting him with an unnecessary dose of poison in the evening. That's how I see it. Does anyone else feel similarly?
I'd have to cite this as about the most subversive thing I do at work. As much as I'd like to be the rebel who pisses in the cappuccino of every bastard customer that walks through the door, I am simply too mature for that. So I pull a little switcheroo from time to time. So fucking sue me.