If your pasta or risotto has seafood in it (vongole, frutti di mare, and similar), don’t ask for parmesan, a server may just decline, and it can come across as taking a shortcut rather than a personal preference.
Cheese is standard and expected on meat- or vegetable-based pasta; the rule is specific to seafood dishes.
A couple of related pasta habits worth knowing:
- Don’t break long pasta (spaghetti, linguine) before cooking it to make it fit the pot — it’s designed to be twirled once cooked, and breaking it stops it from holding sauce properly.
- Eat pasta with a fork only, twirling it against the plate. The fork-and-spoon twirling technique taught at some Italian-American restaurants abroad isn’t actually Italian practice.