Know-it-alls

Do any of you know someone that thinks they "know-it-all"?  I can not stand people like this.  I even often wonder what they think of themselves and if they realize they are like that.  I know a few of these people, they are actually friends.  Luckily though, I rarely talk to them which makes talking to them bearable.  So why am I bringing them up?  Well last night I had the joy as I do monthly to talk with my one "know-it-all" friend.  There are three of us that get together and she dominates most of the conversation.  Her famous line is, "Do you know what I am saying?"  I hate that no matter what you say, you are not right.  There is always something to add or something more that you just do not know.  Worse yet, she is a pessimist.  For example, I was telling them how happy I was that my daughter's orthopedist was impressed with how she walked without her braces.  Instead of being happy for us, she immediately says that my daughters feet are going to start turning with out her braces on and that her feet can change weekly.  Now I understand that my daughter is in a much better situation then her son spina bifida wise, but can she not just be happy for us?  Maybe that is why some people have to refute everything you say.  It must make them feel better.  Perhaps telling themselves that they know more makes them seem more important.  What do you all think?  Has anyone confronted their know-it-all friend?   I would love to know your stories.