Posers who like something because they think it's cool, or to be "part of the crowd". Lamestreamers are the ones who find out about "cool new music".
I'm always fearful of "lamestreamers" liking my favorite bands. Kings of Leon, Vampire Weekend ARE Lamestream. They are the poster children for Lamestream-ness. Please don't start liking Washed Out.
An individual who is not concerned with or even takes pride in the fact that many of his or her interests and tastes are considered by a general consensus as being outdated, uncool, and or unfit for their particular age group. Some people may feel there is a certian appeal to this behavior as it is genuine and rarely posed by anyone who is not indeed lame.
A twentysomething that would find it perfectly acceptable to pruchase items from the children's menu at a restaurant in order to receive a novelty or toy. Jean Teasedale, a fictional editorial contributor to The Onion, would be an example of a female lamester.