If they were in school they would be made to sit apart until the end of term. Barcelona and Real Madrid bring out the worst in each other. Barça, anticipating the opposition's over-physical approach, exaggerate the theatrics. Madrid – and more specifically Jose Mourinho – believe the opposition cannot be beaten at football and so do everything in their powers to stifle the beautiful game.
Mourinho quoted Albert Einstein before the game, citing willpower as the only force greater than atomic power. Another pearl of wisdom from the same genius came to mind as for the fifth game running his side finished a match against Barcelona with 10 men – "Insanity is doing the same thing over and over again and expecting different results".
Barcelona were not blameless. Just as Sergio Busquets exaggerated Thiago Motta's foul in last season's semi-final against Internazionale so Dani Alves helped make sure Pepe walked for a challenge that while a little wild barely made contact with the full-back.
The spectacle as a whole suffered. The watching world had tuned in to see the greatest players on the planet but – Messi's sublime goal aside – the enduring images are of the referee being shielded by riot police as he left the pitch, Victor Valdes having a laser shone in his face, a brawl on the touchline at the half-time whistle and Pep Guardiola urging his players to get off the pitch on full-time as the missiles rained down.
Then there was Mourinho's post-match rant, extreme even by his standards although the topic was wearingly familiar; referees and sinister plans to favour Barça.
"I would be ashamed to have won that Champions League," Mourinho famously said of Barcelona's 2009 victory after knocking Chelsea out in the semi-finals. There was no time to ask him on Wednesday night if he felt Porto's success in 2004 had been stained by Markus Merk's decision to show Deportivo defender Andrade a direct red for a playful kick at his close pal Deco in the final minutes of the first leg, ruling him out of the second game.
Mourinho's record against Barcelona is dreadful. In 15 games his sides have suffered seven sendings-off. His teams have failed to finish their last five games against them with 11 men.
But while Pepe's dismissal might have been harsh and Sergi Busquets' theatrics earned Motta his marching orders in last season's semi-final, the three reds in between were all deserved.
"If you play with fire you get burned," said Gerard Pique after the first leg. "It's no coincidence that this always seems to happen to him." Mourinho has admitted that the battle begins in the press room before the game and this assertion seems to underpin another belief that Barça can't be beaten with just 90 minutes of football.
He creates the hostile environment in which reckless challenges and sometimes reckless refereeing decisions are more likely. His tactics also tend to strangle the possibility of an open football match where the referee might pass relatively unnoticed.
Asked about Real's reluctance to play the attacking football that would have put Barcelona under pressure, one Spanish commentator said: "After Pepe got sent off, Real Madrid couldn't, and before the red card they didn't want to."
Guardiola's side were potentially there for the taking on Wednesday night. The Spanish Cup final had been won by a powerful, positive Madrid too strong for the ever-diminishing resources of their eternal rivals. After that win at the Mestalla, Barcelona lost two more defenders to injury and then had to make do without Andres Iniesta – surely Mourinho would go on the attack in the first leg?
Even Cristiano Ronaldo seemed frustrated by the tactic of letting the opposition have the ball until they approached Madrid's final third. Barça's possession was 82 per cent in the first 15 minutes and before he was substituted at half-time, Real's most naturally gifted player Mesut Özil had made two passes.
Do you like playing this way, Ronaldo was asked after the first leg. "No, I don't, but I have to adapt to what I am told to do," was his revealing response. He was back on-message immediately afterwards echoing his manager's conspiracy theory: "These boys [Barcelona players] have a lot of power off the pitch."
Uefa will deal with that particular accusation over the coming days.