Dear Lio: My top performer is toxic – what should I do?

Dear Lio,

I’m at my wit’s end. One of my best performers—the person I rely on most and get on really well with—is also the one causing the most problems. They roll their eyes in meetings, dismiss others’ ideas, and dominate discussions. When they don’t get their way, they make passive-aggressive, snarky comments, creating an uncomfortable and tense atmosphere. The team is starting to resent them, but I simply can’t afford to lose their results. I know I need to speak with them, but I don’t even know where to start.

– Stuck Between a Rock and a Star

Lio’s typing ...

What a tough spot to be in. Balancing a star performer’s undeniable value against their toxic behaviour is one of the most challenging situations a manager can face. And unfortunately, you’re not the only one dealing with this.

Research by University of North Carolina Professor Christine Porath reveals that more than three-quarters of employees have experienced or witnessed incivility at work and the costs are staggering. A Harvard Business School study found that while a high performer can add around $5,303 in profit to a company’s bottom line, a single toxic worker can cost $12,489 in turnover, morale issues, conflict and disengagement.

But here’s the good news: you’ve already taken the first step by recognising the issue and deciding to address it. Let’s walk through how you can approach this.

Facing the doubt: “What If I make things worse?”

Here’s the truth: avoiding the problem won’t make it go away, it will only escalate.

Reframe this as an opportunity for growth. You’re not criticising them, you’re helping them become better. Focus on what success would look like, such as:

• A high performer who respects their colleagues, listens to other ideas, and uplifts the team dynamic.
• A cohesive, collaborative team where everyone feels valued and safe to contribute.

Write down the specific behaviours you need to address (e.g., eye-rolling, dismissive comments) and the positive actions you’d like to encourage (e.g., active listening, collaboration). Preparation will give you clarity and confidence for the discussion.

Employees who are able to develop this growth mindset are 47% more likely to say their colleagues are trustworthy and 34% more likely to feel a strong sense of commitment.

Taking the first step: “How do I even start?”

It’s tempting to soften the discussion by dancing around the issue but being direct and solutions-focused is far more effective. The key is framing the conversation around their success, not just the problem.

For example, if your top performer has been pushing for a leadership promotion, connect the discussion to their personal career ambitions:

“I know you want to move into a senior leadership role. Developing your ability to bring people with you, and get the best out of others, will be key to your success.”

This approach keeps them engaged rather than making them feel attacked.

Keeping it constructive: “How do I give feedback that lands?”

Vague feedback like “You don’t let others speak in meetings” or “You need to be more collaborative” rarely provides enough clarity for change.

Feedback should be specific, descriptive, and fact-based to help them understand what needs improvement.

Compare these two examples:

🚫 “You don’t allow others to talk in meetings.”

✅ “In yesterday’s meeting, I noticed that you interrupted Sarah and called her idea ‘stupid’. She was visibly upset, left the Zoom call, and it made the rest of the team hesitant to contribute for the rest of the call.”

The second version is more effective because it describes what happened, the impact, and why it matters. It also focuses on behaviour rather than attacking their character, reducing the likelihood of defensiveness.

Listening to their side: “What if they get defensive?”

Once you’ve shared your perspective, open the floor to theirs. Use open-ended questions to uncover potential root causes:

• “How do you feel about how things are going in the team?”
• “Is there anything causing frustration or stress for you?”

If they withdraw, gently encourage them to share: “You seem quiet—what’s on your mind?”

If they become defensive, refocus on shared goals: “We’re both working towards a stronger, more productive team. How can we create an environment where everyone thrives?”

Encourage reflection: “How do you think your colleagues perceive these moments?”

This isn’t about assigning blame, it’s about fostering awareness and collaboration.

Building the road forward: “What comes next?”

Now it’s time to collaborate on a plan for change. Be specific about the behaviour changes you want to see: “I’d love to see you contribute to a more open and collaborative atmosphere. Your insights are so valuable, and I want the team to benefit fully from them.”

Ask how you can support them: “What can I do to help you succeed in this?”

Remember, one conversation won’t fix everything.

The intention-behaviour gap—the difference between wanting to change and actually doing it—is real. Research shows this is why two-thirds of New Year’s resolutions fail, for example. To close this gap, schedule regular one-to-ones to coach, track progress, create the right nudges and reinforce positive behaviours.

How talent leaders can support their managers

Toxic behaviour from high performers can derail teams, yet managers often feel ill-equipped to handle these situations. Talent leaders play a vital role by:

1. Coaching managers on feedback: Provide behaviour change learning on skills like communication, empathy, active listing and more to help them handle defensive reactions with empathy.
2. Highlighting the bigger picture: Show managers how toxic behaviour impacts morale, retention, and organisational goals, emphasising why it must be addressed early.

Want to help your managers turn tough talks into transformational ones?

Our Manager Conversations Solution, featuring Lio, our AI-powered conversation coach, equips managers with the tools and confidence to master even the trickiest discussions. Learn more.