Derail this thread.

You can't derail a thread that's objective is derailing, for by derailing a derailment thread, you are on-topic, and thus, it will not be derailment.

In the same sense, you can't say "It's opposite day!" and be telling the truth. Next time someone tells you that it's opposite day, tell them that by saying that, they'd be telling the truth, therefore it isn't opposite day. Or it is opposite day, and they're then saying it isn't opposite day. They'll tell you you're thinking too hard and you'll say that since it's opposite day that means you're not thinking too hard, but then what I just said must also be a reversal, so I would thinking too hard, even though you just said I was which means I wasn't but then I just said some more things that seem truthful when it isn't opposite day but since it is, it must not be. At this point, they've probably given up the whole idea.