Political debates have a reputation for rattling their participants.

Add NDP leader John Horgan to that list.

After a strong start during the first leaders' debate, as over the course of more than half an hour, he questioned and interrupted Liberal Leader Christy Clark for, as Horgan described it, spewing "alternative facts," things took a turn at the 32 minute mark

The leaders were engaged in a conversation about bridge tolls. Horgan seemed agitated that Clark's answer was going long, to which moderator Bill Good responded he was "trying to be fair."

NDP Leader John Horgan takes questions from reporters following the leaders' debate. (Richard Zussman/CBC News)

That's when it happened. Clark turned towards her NDP opponent — touched his arm and said, "Calm down, John."

It was too much for Horgan.

"Don't touch me again, please. Thank you very much," he said, as he glared to his left at Clark before composing himself and continuing with his answer.

Can Horgan control his temper?

For those watching the debate, it stood out. Horgan with a scowl on his face, as both Clark and Green Party Leader Andrew Weaver chuckled.

Had Horgan lost his temper? Or was he just standing up for himself?

"What would have the response been if I laid my hand on the premier? That is all I am going to say about that," said Horgan, following the debate.

"The premier just wanted to poke and poke. She is physically pushing me. I mean what I am supposed to do? I want to stand up for people, and I will stand up for myself as well."

NDP Leader John Horgan arrives at the radio debate. (Richard Zussman/CBC News)

It's hard to call what happened a push. It was more like Clark pushing Horgan's buttons.

There is a name for this tactic — micro-aggression.

It's something UBC political scientist Max Cameron says was intentional on Clark's part and something, he said, Horgan needs to be very aware of.

"It's more than just an issue of anger. It's a question of how leaders are perceived," said Cameron. "When people look at you, do they have an identification that they can relate with."​

Getting under Horgan's skin

B.C. Liberal Leader Christy Clark is greeted by supporters arriving for the radio debate. (Richard Zussman/CBC News)

What stood out for Cameron watching the debate was Clark's touch of the wrist clearly got under Horgan's skin.

"One of the really hard things to deal with is micro aggressions, because they are hard to catch. That is really hard to deal with. It's not the stuff he can let her get away with," said Cameron.

"I think Horgan, probably because he is big and imposing, has to be very careful as to not come off as angry. He wants to come off as friendly and positive and at the same time he does not want to give in to Clark."

The debate is likely the first time most British Columbians have seen Horgan and Clark interact with each other. But for years they have been sparring in the B.C. Legislature.

During those verbal boxing matches, Clark has often mocked Horgan for losing his cool and having a hot temper. That is why it's especially important now, as people wonder how he would deal with tough negotiations or hard decisions.

"Clark has such a smiling persona, upbeat, so consistent and there are so few cracks in that. It is like a coat of armour and it is very, very effective," added Cameron.

What made this moment unfortunate for Horgan, was until that point he seemed to be controlling the tempo of the debate and was pressing Clark on her answers.

The NDP leader will have one more chance to show he can maintain his own composure.

That is why when the cameras roll during the provincewide TV debate next Wednesday, the NDP leader may be wise to take his opponent's advice and just "calm down."