Huh. I've always mistakenly referred to these as nettles. Actually, I see one of the wikipedia pictures for Bull Thistle is named Nettle.jpg.
I get these (or something very similar) in my yard in Indiana a couple times a year. While spot treating with Round Up is often an ugly affair, for this plant I gladly make an exception. I've never noticed the same plant come back.
If it's already 2' tall, though, cut/mow it first and get it on the rebound. A full 2' plant is too large to cover in a controlled manner.
I'm in Indiana, too, and have always known thistles as thistles. Nettles are a helluva lot more annoying in my experience, especially if there's a big tall stand of them (they're edible!). Thistles aren't so bad. It's easy enough to handle even big ones with a spade (provided you're dressed appropriately). Just push them over with a foot and run the spade through the root from 3-6 inches off center and pull it out. Obviously, if it's gone to seed you're already up a creek for that year. If you have to be dainty about things because it's in a lawn, then my advice is to stop having a lawn.