"Liking yourself at facebook was a phenomenon,because you gain no money from it, so it is just retarded to do so."

If you have a facebook business page it is highly recommended that you go and like your business post with your personal account because more interaction on the post makes it more likely that post will reach more people. It's a highly suggested move for businesses using Facebook. The only reason not to is if you want to avoid people finding your personal page from you doing that. Sometimes businesses mess up and accidentally like with the page instead of themselves and that looks a little silly since company likes company's post but liking the post with your personal account is a good principle to follow as a business on Facebook because it has the potential to increase the reach of your post.

It is a little silly when individuals do it to their own comments etc though.