This word has lots of meanings, but it is mainly used as a negative term for a fashion and music style that though perfectly acceptable is considered bad. This term has been used to stereotype people and deindividualise them(in particular teenagers) as something that in reality does not represent them at all.
Many people claim to hate "emo's" meaning they hate people they stereotype as emo. This makes very little sense, as it means they hate someone for the way they look and the music they like. This does not reflect their personality. Basically, if used seriously emo is a term used by pathetic narrow-minded losers who just have no respect for other peoples tastes and seem to think they know what everyone is like by how they are dressed. They are also stupid enough to think a fashion trend will make someone self-harm.
Most people who use the term emo negatively and seriously are people who can only see the surface of anything as if they actually thought about it they would realise that maybe emo kids are teenagers who were originally generally more emotional/thoughtful/sensitive than most and found the emo fashion and music to fit their taste.
If thats what they like wearing and thats what they like listening to then let them and bugger off!!! They wear it because they like it. Same reason you wear what you wear and you listen to what you listen to, you emo haters are not supreme beings who can decide what is and isn't good taste so get lost you socially conforming arseholes!!
Boy 1: Urgh look it's an emo fag
Boy 2: What makes you say he's a fag?
Boy 1: He's wearing makeup, how gay is that?
Boy 2: He's allowed to wear makeup isn't he? Doesn't make him gay, just means he doesn't conform to his gender stereotype.
Boy 1: Duuuh, what? Your gay... uuur i'm cleffer
Boy 2: Yeah... ok mate, bye!
Scenester is another term like emo used against particular teens for their taste in clothes and music. People have decided that scenesters are arrogant and think they're cooler than everyone else, why they think this? Who knows, probably jealously. Either way it's just another perfectly exceptable taste thats ridiculed and disrespected...great.
Boy 1: Urgh look at that scenester he's wearing tight trousers
Boy 2: And...? What?
Boy 1: I don't know, i just think it's urgh
Boy 2: Oh well, you've shown me
Boy 1: Yeah i know, i'm a stereotypical idiot
Boy 2: Yeah cause you're a disrespectful loser