This is how you are likely to feel if you enage in any of these black hat SEO techniques.

This is an interesting issue – it is possible to destroy your own website rankings and even to get your site de-indexed through a number of tactics. Some of them involved off site SEO and others involve on site SEO, but all of them will require a conscious effort on your part. In essence, these all consist of some obvious forms of black hat SEO.
A Word About SEO
Before we get started, I should point out that virtually forms of SEO currently employed by this or any other company are considered to be gray hat SEO, meaning that they fall in between the strictly approved way to do things that Google likes and the tactics which are obviously used to game the system.
The reason is simple: in an ideal world, Google would like to see your stuff rise to the top through a purely natural selection process whereby people would be linking back to you because they think you have good stuff. They’d also like for you to write material which appeals strictly to humans and which pays no attention to the search engines at all.
The thing is, when you do that, it’s almost impossible to rank high in the SERPs because you will have trouble getting noticed. The reason is twofold: first, not using appropriate keywords and second not building backlinks means your site simply doesn’t get noticed much. Therefore, for all practical purposes, you have to engage in practices which Google may not like, but that they tolerate.
However, while building backlinks and optimizing your on site content with good keyword research is generally considered acceptable as long as it’s done in a non spammy way (i.e. where you build backlinks by commenting legitimately on other’s blogs and you make sure that what you write on your site is keyword optimized but not spammy), these tactics will get you penalized:
Building Thousands of Links for a Brand New Site
You just registered a website with a brand new domain address and you suddenly have 100,000 backlinks all over the Internet, all of them put up in a day or two. How likely is it that you got those backlinks naturally? Pretty much impossible I’d say and so would Google. You’ll find yourself sandboxed for doing this, though probably not de-indexed since it’s possible (though unlikely for a brand new site) you could have been Google Bowled.
Hiding Text On Your Site
Write heavily keyword optimized text in white and then place it on a white background. You have now committed one of the classic sins of black hat SEO and one that Google is well aware of. They can tell that you did it and this practice may well get you de-indexed.
Hiding Junk Text in Code
I saw someone mention this on the Warrior Forum and couldn’t believe the number of morons who were thanking this guy for such a “brilliant” idea. There is supposedly a WordPress plugin which will inject junk code into your documents which Google will see but which your visitors won’t see.
The idea is to make scraped (copied from another site) or PLR (where you and a few thousands others have access to the same material) content appear as if it’s unique to Google. I hope that the people who were thanking this guy for his idea didn’t actually implement it because this is another great way to get your site de-indexed from Google.
Creating a Link Farm
Another stupid idea from a bygone era which some people still seem to be in love with is the link farm. In essence, this is where you have a page on your site with links to other sites, hundreds or thousands of them. In turn, all those sites link to you. The thing is, few people if any visit any of these sites and such tactics are likely to get you de-indexed.
Scraping Content
Finally, those who have a love affair with auto blogs (blogs that gather material from other blogs) are having a very tough time with the new Panda update. While it’s okay to have occasional material like this (assuming you have permission of course), having a blog with no unique content is a sure way to get yourself ignored by the Google search bot.