Mail.app, show me a plain text!

I hate HTML messages. Especially, when you ask your mates not to send HTML for simple text. They do. You won't shoot em, because you will have to do their job as well (this leads to lack of sleep). So there is other way: force Mail.app display a plain text. Normally, there is no checkbox in Preferences, but Mail.app still "eats" this preference in plist, like this:

<key>PreferPlainText</key>
<true/>

Cool. So we can do this:
defaults write com.apple.mail PreferPlainText -bool TRUE

Now restart Mail.app and you've done.