If you're a parent of twins, you'll have lots. My favorite is when people ask me if the girls are "natural." I like to respond with, "no, they're actually robots." Another fun way to answer is "well, late one Friday evening after my husband came home from work, we were feeling pretty frisky...," that shuts them up pretty fast. I am still not sure why total strangers want to know about others' fertility, and I don't THINK parents of singletons get asked this question. Correct me if I'm wrong!