this seems crazy to me. how can any professional working today not use linkedin? When we get new employees into our office from the non-tech world and they don't have a linkedin profile, they are slightly mocked - like, let with the times buddy.
That aside, people who judge others by their (non-)use of social media are the worst. Someone who mocks friends for not using facebook is not a good friend. Someone who mocks colleagues for not being on LinkedIn is not a good person to work with.