There's a few reasons why taking the virtual world seriously - at least at certain times - is beneficial.
Think of it that way: People you don't know in RL will not want to talk or get to know you since they think that you're a jerk offline as well. Might be true or not, I don't know you offline, so I can't judge it.
Furthermore, discussing or interacting online is not laughable or stupid. I have made very tight friends through the internet, people I would trust more than a lot of people I got to know personally. Most of them I met since I got to know them, some not yet, but I intend to.
If you intend on meeting these people offline (and I suppose you do at least in the European cases), you should respect them and not hurt their feelings. Behaving bad online will shed a bad light on you and make you unliked before you even got into personal contact with these people.
To give you a perfect example. In the German Smash community, there's a player who - actually similarily to what you did - trolls and flames a lot, puts out only attacks, attacks the person themselves instead of their points, etc.
He went to a tournament. Absolutely nobody wanted to talk to him, and he said not a single word the entire tournament. A friend who met him there shaked his hands out of politeness, but went to wash his hands the second they were finished. And all based on his online behaviour.
The internet has become a serious way of communicating and has overtaken telephone and letters by far now.