I'm not contradicting because a certain percentage of parents can be over the top, but I think you can be proud of your kids achievements and brag about them without putting others down and being psycho. Clearly you have run into some who can't do this.
I actually like to hear parents go on about their kids. And are they living through their kids? Yes, to an extent, but aren't we also doing that when we are proud of their academic acheivments (and pressure them to do well) and when they get good jobs or marry well (whatever that means)?
As a coach the ones who really got to me - were the parents who could never show up to see their children play. Those kids know who is in the stands - even the coolest of the cool are looking out to see if Mom or Dad is there to see them.