The 'Spaced-out-you-mean-nothing-stare' Syndrome

I don't know if this has ever happened to you, but whenever I'm introduced by my friends to someone they know -be it in a party or gathering of some kind- I usually come across somebody who in the beginning might say 'hi' and may look all enthused about wanting to start a conversation, but later as I start talking to them they begin to stare blankly at the universe around them in a sort of contemplative fashion - and then that's when I lose them completely. They spot another person in the crowd and begin asking them a question that suddenly entered they're minds - tuning me out abruptly as if I was some sort of staticky frequency over the radio. I don't know if it's an attention span disorder that they suffer from, or if it's me and I have a 'don't-talk-to-me-sign' sticking out on my forehead. If you notice from the two pictures that i included in this post, both of them are looking elsewhere as if a deep trance had overtaken them, or as though they were searching for the meaning of life. Whatever the case, I think you get my point..