1. Never, under any circumstances, assume, state, or imply that a Puerto Rican is not a US citizen. The island is a commonwealth of the United States, and if you suggest its sons and daughters are immigrants--especially (shudder) Mexican immigrants--the Puerto Rican you are dating will chop you up, season your remains, and roll them into delicious pasteles. I know it's difficult to wrap your mind around the idea of a brown, Spanish-speaking American citizen, but you just have to take it on faith.
2. Never, under any circumstances, assume, state, or imply that a Puerto Rican is a US citizen. Though a commonwealth of the United States, the island has its own unique, vibrant, fiercely independent cultural identity. Suggest otherwise and the Puerto Rican you are dating will subject you to a sermon on American imperialism, a fate worse than being chopped up and served in cannibalistic pasteles.
3. Never, and I mean never disparage one of the following: salsa singer Héctor Lavoe, professional famous person Jennifer Lopez, or the coquí, a noisy little frog that Puerto Ricans adore beyond all sense of reason or proportion.