Fill a large pot with water and bring to a boil. Generously salt. Add the broccolini and cook for 1-2 minutes, until just starting to soften.
While the broccolini is cooking, heat the olive oil in a large skillet over medium heat. Add garlic and chili flake. Stir. After the broccolini is done, transfer it to the sauté pan. Continue to stir, coating the broccolini in olive oil. Taste and season with salt as necessary. Cook for 2-3 minutes, turning the broccolini over in the pan, making sure the garlic doesn’t burn. Add the red wine vinegar and cook for 1 minute. Remove pan from heat and let the broccolini cook for 1 more minute in the residual heat leftover in the pan. Taste for seasoning and add more salt if necessary. Serve immediately or at room temperature.