Bad stuff. (Photo courtesy Flickr user solidstate

In an official blog post Tuesday, YouTube announced that it had enacted a new set of guidelines to sanitize its most viewed lists by cracking down on videos with "profanity" and "sexually suggestive" content.

The changes, YouTube wrote, are meant to "help ensure that you're viewing content that's relevant to you, and not inadvertently coming across content that isn't."

Let's remember first of all that YouTube has had trouble luring big bucks from advertisers, and so this clean-up undoubtedly has two eyes on the bottom line.

The way it works: If a video violates the guidelines, it will be demoted -- removed from the front pages and marked as "age restricted" -- so only registered YouTube users who claim they're over 18 can watch. YouTube's Most Viewed and Top Favorited pages are often where videos go to become mega-viral sensations, so if you want your vid to qualify for this viral launch pad, you'd better not break the rules.

That is, if you can find them.

YouTube is specific about what it means by sexually suggestive. But it says nothing about what profanity might mean in practice. (The site offered a similar nondefinition back when it banned drug-related videos.) Staying mum is a PR tactic, of course, because obscenity and profanity are notoriously fluid and slippery concepts. Any attempt to nail them down will bring a wave of examples the definer forgot to outlaw, or couldn't foresee. And that's why the definitions you do see ...