I never said anyone said he was right to do it. I said they were offering mitigation, making it a stupid, but less stupid thing to do than it was.
If you're frustrated and snap, you actually snap, you don't do something half arsed like that. If he'd snapped it would have been a much bigger incident as he would have been trying to actually hurt Lascelles, and then there'd have been a full on brawl. What he did was an intimadatory act, a threat that he'll do something if Lascelles keeps going, it's not a "snapped" act. To do that you're still exercising control, if you're still exercising control then it's a conscious decision not an instinctive one, so then the only explanation is stupidity.
He did snap. For the third time, Lascelles poked his head into Mbokani's face, and Mbokani snapped by lunging forward to butt his head. If someone came up to me on the pitch in a heated situation like that, I either nut them or punch them, but neither of those is any more or less calculated than the other.
At least you're still in control of your frontal lobe. People can have levels of rage as they learn to control it (often through imposed discipline - like a football referee); some don't learn and snapping can be ugly and unrestrained. You are far closer to the truth, good to see you in control. 