I have been plagiarized by this site.
It is an exact copy of my post.
It happens.
There's a few things you can do to "discourage" it.
1) Write a quick plugin that adds a Copyright notice to the beginning of a feed posts content. Suggestion: Randomize its output, else it "could" be stripped out.
2) Get that site shutdown. Contact their ISP, and let them know that a site they host has violated their TOS by committing copyright infringement.
3) Find out their IP, and block it in your index.php file. (Or instead, send them a "fake" rss feed, with some nasty grams in it.)
Angusman has a feed copyright plugin, but you may wish to modify it a bit so the copyright comes out first, vice last.
They've been shut down now, it seems. :)
So it seems :)