trolling is posting with the intent to rile up other users. Typically this is done by posting without any real facts, or not making it clear that it is your opinion. Also, just stating that something sucks would classify as trolling.
So, you say PS3 rulez and wii sucks and is a kiddy console. That is trolling even if you state that it is just your opinion, as it adds nothing to this website, and instead all you do is get other users upset. You can word things differently like, I prefer the PS3 because it has the games I enjoy better than the Wii. (note, I really like the Wii and Nintendo better, this was just an example 
)
If you make a controversial statement but back it up with sound reasoning or show facts, then you are not trolling but intelligently posting which is appreciated even if we may not agree with your point of view.
EDIT: in your case you probably got the warning because of the "fail" added to the end of your statement.
