NIMBY is only perceived as a pejorative term or an insult because the people engaged in NIMBYism are being called out on their shitty behavior, and they want to hold onto the illusion they aren't being shitty. The term itself is nothing more than an accurate descriptor of people who don't want new things built near them.

FlavioSuave: What about homeless people who engage in "shitty" behavior? Can we have an derogatory name applied to them by the media?