A slightly over-the-top title, but there are so many threads about when to put money in the market that it's time to blow up this irrationality.
First, statistically and rationally, you should put your money in the market as soon as it's available. The market goes up over time, it is more likely to be up than down on a given day, and you can't time the market successfully to know which days are which, so play the odds and put your money in as soon as possible.
Second, nobody here actually believes in dollar cost averaging. Many think they do, but because of a logical error that is easy to make but completely wrong. The dollar cost averaging argument goes something like this: I have $100,000, and I will put in $10,000 per month for the next 10 months (or whatever time frame) so that if the market suddenly drops 50%, I won't lose 50% on all $100,000.
That is not probabilistically the best approach (see the first point), but the rationale behind it is clear--the idea that you're avoiding a major loss on all the money. The real problem, though, is that nobody actually believes in the second approach. Here's why. Every day you have any money in the market, you can pull it out! Every day, you are effectively making a decision whether to invest "all" of the money that you currently have in the market.
How many posts about dollar cost averaging have you seen that say after you complete the $100,000 investment (after 10 months or whatever), NOW pull the money out and start all over, $10,000 at a time. Why not? It's the exact same logic. You have $100,000 that you can invest all at once (indeed, it's already in the market!), or you can pull it out and dollar cost average.
Yes, there might be slight tax consequences, but that's not the logical error here. Every day that you have money in the market--that you KEEP in the market--you are making a decision to invest it rather than pull it out. And unless you are constantly pulling the money out and dollar cost averaging it back in, you do not really believe in dollar cost averaging.
This is important because it highlights that the correct answer for everyone is to invest money in the market as soon as the money's available (consistent with asset allocation, etc.). Even for those who instinctively lean towards the idea of dollar cost averaging, realize that not only is it irrational, it is not something you really believe in because you would not take out the money that's in the market and dollar cost average it back in. So if you're not really committed to an irrational idea, there's no reason to do it in the first place.
Finally, this advice ignores the market timers. But really, a market timer doesn't dollar cost average in either because there's no reason to do so if you can predict when the market is up or down. You then just invest all at once when "the signs" tell you its time.