On an adult level, one nasty instance of the socialization issue was at a party within a small ring of almost-acquaintances. I mentioned that my sister-in-law was homeschooling her only child, and possibly even mentioned that we were thinking of homeschooling our only child. One of the men just about bellowed how he could never do that to his only child, who needs to learn how to get along with others, and she'd never get that through homeschooling because she has no siblings, etc. He was very loud, long, and adamant; I was utterly unprepared to respond and embarrassed.
Then there is the "good for you" response. When I say that we homeschool, I detest hearing that phrase. This is a reply I've heard a few too many times, and right or wrong, it sounds like "well, whoop-dee-do", as if I had just bragged that we have a regular Harvard and Oxford going on in our house. I never know what to say after that.
Most often though, I've overheard this type of thing between my daughter and a friend, who's in public school and in the same grade as my daughter: "You don't know division? We had that last year!" She went on to state division facts. These are 9 year olds, she wasn't being rude on purpose, and her parents weren't there to admonish. Usually in these cases, I resort to educating the other child by saying homeschooling means that we can go at our own pace, and while we're working behind in areas, we're working ahead in other areas. (The way it should be! ;))