The definition of "threat" is to express an 
intention to hurt or harm. By saying:

>I said i know cels people and will 
try and make sure nobody buys from him again. 

You are most definitely threatening him by 
expressing an intent to harm his business.

As for the stupid comment, I got that directly 
from your first post which said:

>Then I e-mailed him 3 days ago talking about him 
not responding to me, and it was really stupid to 
do that 

Wes, I'm not trying to be a smartass. Honestly. I 
think your intentions are good. This guy's a 
complete idiot in my book. Let's do all we can to 
warn people about him, absolutely. But by telling 
him you intend to harm his business because he 
isn't returning an email, you're only stooping to 
his level. The only way to express your anger is 
to simply not do business with him. 

That's it!

-MeganD.