How's Your Lame Detector?

We've all experienced this many times during the courses of our lives, and depending on our social circles, possibly on a daily basis:

You get caught into a random conversation with someone, like a friend's friend, an acquaintance, a clear-skies friend, or even a close friend, and he starts droning on about something neither you nor anyone else within earshot cares about in the least. The lameness of what he is saying is blatantly obvious to everyone in the group, except him. Sometimes you manage to change the subject, or divert the conversation in another direction, but sometimes you get stuck listening to him go on and on, uncomfortable with revealing to him how lame he's being.

It's easier to deal with that kind of situation when in a group, but this may happen when you're the only person listening. That's right, let the various memories of boring time wasted flow back to you. It sucks to get stuck in that situation.

How can this person not realize how uninteresting he's being? How could he have no ability to detect my level of boredom, if not his own lameness? Could he be you?