I suspect Rigby thinks he/she is being really clever and superior to everyone else - in fact they are just a tiresome child.
Some people are just made cross I guess. Maybe when they write their thoughts down it comes over as a bit more cross and argumentative than if we could have heard the intonation in their voice - but they should take that into consideration. I don't mind having a difference of opinion with anyone, but as I always told my children - if you can't say (write) something nicely then don't say anything at all.
I was just watching the GP programme on TV and a young girl was so cross that the doctor advised her to go up to the hospital and appeared very ungrateful for any help that was being offered. There is no excuse, whatever kind of bad day she might have been having.