None of you who know about SAO have called Alivaril a Beater. You should be ashamed of yourselves.
For those who haven't seen the series, Beater was a derogatory term used to refer to players who had played the Beta of SAO and thus knew a lot more about how the game worked than everyone else, who used that information to gain unfair advantages. It's a mix of 'Beta Tester' and 'cheater', and was originally directed at Kirito, who had reached floor 10 during the Beta, something no other Beta Tester managed, apparently. Because of course he did. Anyway, Kirito apparently decided that he needed to take all the hate for the Beta Testers onto himself, so he started bragging, and thus the term was born. Because, again, of course he heavily influenced the lexicon of the players stuck in the death-game.