There is no "code"
I've seen muggings from he 70's and 80's that make this incident look like kissing. Thornton went over the line, but that's always happened in different eras as well. You can't take that out of hockey even if you neuter players like Thornton. Hockey players in bad moods sometimes go over the line.
Orpik didn't help himself any by being Brooks Orpik, one of the most disliked defenders in the league.
I must disagree in that for a long time there absolutely was an established, albeit unwritten, code. It died when the instigator rule came in. Sure, back in the guy some guys were playing on the edge or over it, but they knew they would have to answer the bell for it later on. That doesn't happen anymore. That coupled with the increase in equipment protection has led to complete disrespect amongst a lot of the players.