I guess he didn't get the tax refund he was expecting.

I'm with Ken and Wolf, but I would take it a step further. If this were a Muslim who slammed his plane into a government building because he was angry about our policies in the Mideast, I don't even think that would qualify as terrorism. Terrorism has a purpose of using fear and violence of achieve some political objective. If you're just lashing out at something that you hate, that's not terrorism. It's disenfranchisement, desperation, despair, anger, but not terrorism.