This isn't a case of "I just want to come and pray and leave, please don't bother me."
This is a case of, "I am refusing to notice someone who is relatively new; I've seen him around here so he's not not a total stranger, but I'm not going to make any effort at all to even say hello when our eyes meet and, instead, I'm just going to socialize with Joe and Maria here."
The first I can sympathize with; that's me most of the time, especially in an unfamiliar place. The latter, however, is unconscionable for a Christian. I am socially awkward at the best of times and not very outgoing, especially with strangers, but to see someone being uncomfortable, sitting all by his lonesome during coffee hour while everyone else is socializing (note, this isn't some Old Country parish where no one is socializing...it's happening all around him), I would at least say hello. No one is saying that you have to be best friends with everyone in your church, but to patently and obviously avoid someone is rude, especially in the United States.