Boil large pot of water to cook pasta. Salt when boiling.
Cook the pasta and rapini together in the same water and pot.
When pasta and rapini are almost done (approximately 10 minutes), put the olive oil in small frying pan. Get it hot, add the garlic and red pepper flakes. Let it saute for about 3 minutes until the olive oil has been infused with the garlic.
Drain the pasta and rapini. Put in a large bowl, pour the olive oil mixture over the pasta mix. Add salt and pepper and garnish with 1/4 c parmesan cheese.