I am not sure what it is but some people take on a totally different persona once they get behind a keyboard. They do and say things that they would not dream of doing in a million years in their offline world. Yet the paradox is that the activity online is more likely to be discovered.
The powerful search facilities plus the speed of communications means that if you do anything radical online it may come back to haunt you. Imagine the scene. You have a sales meeting arranged. Your prospect wants to find out a little about you so she types your name into Google. Back come links to some of your blog entries on other sites where you have been a little aggressive or using foul language. Do you think that is going to affect what the prospect things about you?
It may seem like a bit of fun but you need to remember that if it is indexed by Google and other search engines it can be found. Even if it is not then it could get found anyway – for example on sites like FaceBook.
As a golden rule, be the person online that you are offline and at least you will not have any surprises!