In a large pot, bring 6 quarts of water to a rolling boil and cook the pasta according to package directions until al dente—linguine will take 10 to 12 minutes, thinner pasta a little less.
While the pasta cooks, heat the oil over medium-low heat in a saucepan large enough to hold all the pasta. Add garlic to the oil and cook very gently, just until the garlic softens and starts to turn golden—do not let it brown. Add chili and optional parsley, along with a ladleful of starchy pasta cooking water. Turn the heat up a notch and let the sauce simmer vigorously for about 5 minutes. When the pasta is almost done, drain in a colander and turn immediately into the pan, mixing the pasta together with its sauce. Let simmer for about a minute or two, then serve immediately with more salt and ground pepper. Parmesan, too, if you're me.