To behave like a jackass without realising it. To beleive and act as if you are all knowing when in fact you are clueless. To debate for purpose of debating without the possibility of admitting yourself to be wrong. To disregard someone without a valid authority for your mental triumph.
"I know everything there is to know, i read a something on ynet about it so it is impossible for me to not be right" - this guy is being a razlubinsky
A: "did you know that the ancient men were like 5 ft tall at most?"
B: "5 ft at most? let me check - omg i read about some ancient man who was 5.2 ft tall - you are so stupid and make up everything"
A: "well everytime there are few who break the chart..."
B: "no, you said 5 ft at most so you are now wrong and a liar..."