Have you noticed? Geeks don’t touch. I noticed this in myself a while ago, and have since been watching other geeks to confirm my theory. I was at the Boston Ruby User’s Group a week ago and essentially no-one touched. When two geeks are introduced, unless it’s a somewhat formal introduction like an interview, we don’t shake. When we encounter each other, or go our separate ways, there’s no casual touching. Many will actually wave at each other in greeting from a few feet apart so as to avoid the simple touch that normal people would expect. I think this is a byproduct of the fact that so many developers are autistic regardless of if they realize it or not.

…Some may even be pathologically sensitive to loud noises (as some people with AS have hyperacusis), strong smells, or dislike being touched; for example, certain children with AS exhibit a strong dislike of having their head touched or their hair disturbed while others like to be touched but dislike loud noises. - Psychology Wiki

I wouldn’t say that most geeks are “pathologically sensitive” to touch but please don’t think that the geek in your life is being antisocial, or intentionally rude, or anything like that if they eschew the common social touches. I think that most of us just don’t like to touch anyone who isn’t particularly close to us emotionally.