You can't disable the "like" feature on the top bar when you are logged in, but you can opt out of having the "like" button under all individual posts:
Appearance —> Extras —> uncheck " Show a like button and who has liked my post on all of my blog posts above the comments section" —> Update

To turn off "like" on only one post at a time:
Edit Post —> scroll all the way to the bottom —> uncheck " Show likes on this post." —> save draft or update post.

I thought that I would try out the "like" system on my own blog. To avoid appearing narcissistic is there a way to "unlike" my own post?

You can "unlike" posts by going to Posts I Like (http://wordpress.com/#likes) and de-selecting them there.

Also, this seems to be very similar to ratings, which could confuse people who wouldn't know whether to like or rate a post. Ratings also give you a better idea of how much people like or dislike a post or comment. Is it possible to disable the "like" feature for your blog to avoid this confusion. I'm not sure if I want to yet but it would be good to know.

You can remove the button from the bottom of your posts by using the toggle in Settings > Extras (or you can turn it off for individual posts by using the toggle in the post editor).

Also, this seems to be very similar to ratings, which could confuse people who wouldn't know whether to like or rate a post. Ratings also give you a better idea of how much people like or dislike a post or comment. Is it possible to disable the "like" feature for your blog to avoid this confusion. I'm not sure if I want to yet but it would eb good to know.