Mr. Robineau is the faculty advisor to the "Hot Seat" television show that Leo and Kevin run, and if we may say so, he's not exactly stellar at his job. The show is so well organized by the responsible duo of Kevin and Leo that Mr. Robineau does not really have to do much at all except show up.
Unfortunately, this means that when it's Stargirl's turn on the "Hot Seat," Mr. Robineau is not on his toes, and misses the fact that the jury members are verbally attacking Stargirl with cruel gusto. To give him some credit, he does eventually end the attack by stopping the show and destroying the tape. But it's too little too late. The damage has been done, all thanks to Mr. Robineau's laid back style.
If Stargirl's character gives us an example of the benefits of being observant, than Mr. Robineau shows us the price we pay for not paying attention. See, if we're not paying attention, people can get hurt, like Stargirl does on the "Hot Seat."