Forgot to mention, I removed all infected leaves and lower branches (if that's what you call them) yesterday before spraying. The spots in the pictures developed overnight.

I don't know what it is, but tossing the plant seems extreme, it looks pretty minor to me. Plants get stuff... it's gonna happen.

You're totally right that it's pretty minor right now. I was just concerned about it spreading to all of my plants. I would really hate to get rid of it, but I'd do so if I had to. Since it's in a container, maybe I'll just move it to a location away from the others.

That is possible, but as it doesn't look like something really serious that will ruin your crop (though I could be wrong as I dont know what it is), I would wait and see how it develops, unless you have more than enough other plants. I know if I tore up every plant at the first sign of any trouble, I would not get any tomatoes. JMO...

Well, after moving the plant to the other side of my backyard and spraying it with copper after each rain; I ended up removing the plant and trashing it. The spots kept spreading until pretty much every inch of the plant was covered (apart from the central stem). However, the spots never really grew in size. My GUESS is bacterial something.

Now my other plants are starting to develop spots as well. I'm kind of at a loss. Hopefully I can save the others somehow :/