To me, these two idiots clearly were trying to be funny. I would've kept walking, just as the delivery guy did. He was walking away, but then turned and shot the prankster who kept following him with the phone. Again, I have no sympathy for these pranksters, but we'll have to agree to disagree on whether it was self-defense or not. The jury sided with you.
I don’t blame you for thinking how you think, but when I see the twitter video you linked, it’s only potentially funny from a distance to me.
Imagining the scene’s point of view from the vic’s position, and given the rather serious and pissed off look on the perps face, I can’t reach that conclusion. If they were smiling and laughing while doing it it would indeed seem more like a bunch of punk kids just being obnoxious, and I’d have a different opinion.