Ami, you got it in one. It's a very subtle, very insidious form of enemy creation. The underlying message is "you're not one of us, you don't like what we like or value what we value; you are not truly welcome among us; and we are going to assure this by creating a fake personality for you, that we can take pot shots at."
The thing is, this kind of behavior is just insane. Read that description. Sane people don't do this kind of stuff. But... people in groups... from little bitty dyads to entire countries... do this kind of stuff. All. The. Time. Kindergarteners do it, Prime Ministers do it.
Beth, I wish I had a magic wand for you on this one. All I can say is that seeing this stuff clearly will take you through the stages of grieving... there may be a point where you just can't stand seeing them pull this stuff, and then there may be a point where you just can't stand seeing them, period, and then later on there may be a point where you have the kind of reaction Write describes on the "Aha" thread... where basically you see it, label it accurately, are detached from it, and can decide if seeing them is worth the effort it costs you, on a case by case basis.
But you will never be able to fix it or get through to them. It's a 'gang' thing. Gangs need enemies, they need that adrenaline-boosting group reinforcement. If they can't find enemies legitimately, they will manufacture them. It will fix itself if and when they value relating to you more than they value being a gang.
PS: Letting them know you see through the shenanigans may be satisfying, and it may be a necessary step in separating from them psychologically, but don't expect it to 'get through' to them quickly, if at all. When a gang-group's identity is threatened it just intensifies the group's determination to exclude the threat, in the short term anyway.
PSS: Hi lighter. I hear you

. Ignoring is just a tactic... like all tactics, when properly understood it normally tells you more about the ignorer than the ignored. Doesn't make it nice to put up with... but understanding definitely helps.
PSSS: Changing, yes, it is groupthink, Gang style!