Autopromotion means activity practiced by fanboys and fangirls on forums promoting their favorite products for free without getting paid.
Autopromoter doesn't usually start problems, insult, or hurt others or use foul language. He is trying to advertise directly and talk to people directly explaining why it is better to have his "this" favorite instead of "that" other product.
Also see trolling
1. I am getting tired of reading this fanboy's autopromotion messages about Xbox 360.
2. I don't like the way he autopromoes Playstation 3 on my forum.
3. So what if I autopromote my favorite games? They are the best games in existence because...
4. I hate autopromoting people like you.