Ha? What are you talking about? Why is this famous? But actually I have seen this a lot lately since I knew about yaranaika?
Technically, this has nothing to do with yaranaika, but it has a scent of that kind of thing…If you follow 2ch or Nico Nico, you might be possibly sure of this. But before I explain this, let me teach you how it should be pronounced.
As you can see, this is not written as アーーーーーッ！[Aaaaagh!] but アッーーーーー！[A,——!]. Too difficult! Okay, take a deep breath first, and just say あ[a]. Please end it immediately after you said あ. Do not shut your mouth yet, please pretend to continue so that anybody else can’t say anything. Umm, is my explanation okay? To be honest, I think no one can teach it well!
To get to the point, this weird shouting is to describe when a gay gets poked. Now you can see アッーーー！ easily since it has been an internet slang. At any rate, this is based on the Japanese baseball player, 多田野数人[Kazuhito Tadano] who succeeded in joining the Major League in 2004. Actually, he showed in the gay porn video with his juniors at school before he got a fame. At that time, some gossip magazines told the rumor temporarily, however as soon as he went to U.S., the rumor started to spread out.
After all, he had to admit he actually showed. According to him, he had to do that for money…Anyway, this became a fuss among 2ch bugs. This is also called TDN事件[TDN Incident]. TDN stands for his surname TaDaNo. Perhaps, you could see some screenshots from the video on 2ch or elsewhere. アッーーーー！is actually what the baseball player uttered when he got poked. The most famous conversations are 「四つんばいになれ！[Get down on all fours!]」「やれば返していただけるんですか？[Can you release us if I did it?]」「アッーーーー！[A,——!]」「気持ちいいんだろ？オラ、気持ちいいって言え！[You feeling good, eh? Say feeling good!]」「気持ち…いい…[Feeling good…]」
Oh, poor him.