Preheat oven to 200°. Place a medium-size heatproof bowl in the oven to warm while preparing the salad. Trim off the base of the root from dandelion plants, leaving plant intact, then carefully wash under cold running water, spreading the leaves at the base where earth often collects. (If using giant commercial leaves, wash, then cut them into 4'' lengths.) Shake water off leaves, then pat dry with paper towels and set aside.
Slice bacon into 2'' x 1⁄4'' batons. Put bacon into a small pot, cover with cold water, and bring to a boil over high heat. Reduce heat to medium and simmer for 5 minutes, then drain. Heat olive oil in a small skillet over medium-low heat, add bacon, and fry until about 2 tbsp. of fat have been rendered and bacon is lightly crisp on all sides, about 20 minutes.
Put dandelions into preheated bowl, then add bacon and its rendered fat. Return skillet to high heat, add red wine vinegar, and bring to a boil. Using a wooden spoon, scrape any browned bits stuck to bottom of skillet, then pour over salad. Season with a little salt (keeping in mind the saltiness of the bacon) and lots of pepper. Toss salad and serve immediately.