Did Eric feel dissed?

Every day on the streets of America, boys and/or men die because other boys and/or men near them think that they are being "dissed" - disrespected. There are neighborhoods where, if you look at another guy in the wrong way, he might pull out a gun and shoot you.

Did Eric feel "dissed" by the other kids at Columbine High School? Was he dissed by the bigger boys who shoved him around? Dissed by the kids who never treated him more senior or let the weird-looking Eric kid come along? Dissed by the girls who never called him back and/or made him look like a fool?

Was going NBK the only way he could show the world that you don't diss Eric David Harris and get away with it?

Or was there something else going on?

Nope, that about sums it up. One reason he went NBK was because he had a sense of self entitlement. He felt like he wasn't getting what he deserved and therefore, he threw a tantrum. 'I'll show those fuckers for leaving me out of so many fun things and those girls who never called me back'.

I think he most definitely felt dissed. [You must be registered and logged in to see this link.], I like how you describe NBK as a tantrum,
though I'm sure Eric would hate that description. He wasn't some bad ass "natural born" killer
He was a just some punk kid who felt disrespected and lashed out at everyone.

in short, absolutely.

Sick little sociopath that was going to show everybody & make them pay.

That sounds about right (or at least right about a large part of it). He felt dissed and humiliated, and he believed that he deserved better. He wanted to stop this, and show that he was the alpha, whilst seeking revenge on those who he felt had wronged him.

Oh yes I'm he certainly felt disrespected. Though I don't think it was "dissed" in the way the media associate with urban, gang-related and mostly black or latino US males.

I think "underappreciated" would be a better description as far as Eric goes.

One thing that's very obvious from Eric's writings is that he (especially during the last entries of his diary) had gripes with people who were close to him, people he seen as buddies or just good acquintances. I'm not sure who it was specifically, but it were certainly his "buddies" rather than random kids in chs that bumped into him in the corridors or wrote stuff on his locker.

Eric had a sense of entitlement and a high opinion of himself, and it seems to have pissed him to no end when people did not treat him seriously enough, did not invite him to a party his other friends attended etc.