SAN JUAN, Puerto Rico — Bananas grow so well in Puerto Rico that people are constantly giving them away. My neighbors in Old San Juan will go out to the country for the weekend and start knocking on your door come Monday, asking if you would like a bunch. Saying yes can be dangerous, I’ve learned, because you could find yourself with 10 pounds of guineos niños, also known as ladyfingers. That’s more than enough for four loaves of banana bread and a daily burst of potassium in the morning’s oatmeal. It’s more bananas than anyone really needs. But the bananas keep coming.