For me, when you think about it, the turning point of Arsene's abilities and general mentality at Arsenal began to drop off all started with that 4-4 collapse at Newcastle in 2011. Perhaps you could point to earlier moments but that game was pretty bad.
Soon after, we fucked up that final against Birmingham which is still one of the worst defeats and feelings during his time at Arsenal. And then of course to rip the fragility further, the famous 8-2 defeat to Man Utd a few months later suddenly put him under a lot of pressure.
2011 was definately the first point of some fans wanting him to go. The fact it's now taken as long as 6 years to finally get to the stage where it's gone from one side to the other, while experiencing further pain shows we've put up more than enough crap in this time and it really has to end now.