I try not to generalize....but from personal experience....I have noticed that young Christians (like, under the age of 25?) aren't "awkward" so much as they are just quietly condescending.
I think this is it for me personally. I'm 29, but a lot of the people I work with are straight out of college. I'm not sure its condescension, but it does kind of feel like they struggle to talk about things other than religion.
I really just think it is a "certain kind" of Christian that is socially awkward. I mean, technically our country is full of them, but most normal people are really low key about their religion so they act like any secular person would. But the "certain kind" of Christian is like a "certain kind" of any sort of fanboy and make everything about their religion. That kind of person is obviously not going to mesh well with normal society.
I never considered the autistic implications there. This is particularly interesting because I am working at school for special needs children.