I doubt you would know about it, but once upon a time, if a player headbutted another, then the receiver knew about it, none of this wiping your sweat on the forehead of your opponent that we get today, I'm only surprised Nasri didn't fall the same way Vardy did.
Quite a long time ago Dennis Tueart was given a torrid time by a lower league player in a cup tie, and when he eventually snapped, he headbutted the twat, and was rightly sent off, but the other player was also sent off, whilst on the stretcher that was required to carry him off, and he spent a couple of days in hospital for his efforts.
Nasri is, and always has been, a shithouse, much like Vardy, if both had played in those days they'd have been very very quiet, in fact neither would probably have made it in football at all.