It's easy to lose your cool when someone is being disrespectful. But in these types of moments it does more harm than good. Remain calm and respectful when addressing the employee, regardless of how they react. A shouting match gets no one anywhere.
Don't assume the reason behind the action of a difficult employee. Get to the bottom of it. Listen to what they say and clear the air. Sometimes the company culture may very well be the issue not the employee, but of course there are times where it is definitely the other way round.
It's not all about what you have to say, it's very heavily dependent on what they have to say as well. Listen to understand what they're saying. Acknowledge their feedback and concerns. Just listening can have a great positive impact on their behaviour.
It's very easy to have a negative perception of the employee you're handling. Remember that there is always a reason why they're behaving the way they are. Be fair and don't be too quick to judge. Be patient and kind in your approach, you never know what someone is going through.
The goals are to improve the situation and employee's behaviour. If you've done all you can and there seems to be no changes in them, know when to cut your losses.
Stay calm and be respectful
Learn the core issue
Listen to what they have to say
Be unbiased