You can't fake your way through a difficult conversation

"No amount of preparation can save a confrontation if the person who brings up the failed promise isn't in the right frame of mind." 

Crucial Confrontations by Kerry Patterson, Joseph Grenny, Ron McMillan, and Al Switzler

You can't fake your way through a difficult conversation using fancy techniques while simultaneously not letting go of your underlying belief that the other person is a moron.  You will leak that belief through both verbal (word selection, tone, etc.) and non-verbal (posture, mannerisms, etc.) cues.  I suppose theoretically you could train yourself to hide all your cues but it sure is a lot easier to work on your thoughts first.

A simple model that describes what happens:

Note that this process happens in a matter of seconds, if not faster.

Your main opportunity to improve is at the Tell a Story step:

What's the actual problem?  Is it the Content of what just happened? Is it a Pattern of behaviour? Is it a loss of trust threatening the Relationship?  What are the Consequences of this problem to you? your relationship? your task? your stakeholders?  And finally a very important point is to be careful about assumptions about Intentions, that is, why the person behaved that way.

Why is the problem happening? Humans tend to assume that the primary reason for someone's behaviour is their internal disposition.  This is known as correspondence bias.

In the classic experiment by Jones and Harris, subjects were asked to read pro and anti Castro essays and then judge whether the writer actually had a positive or negative attitude toward Castro.  Obviously the subjects assumed that a pro-Castro essay writer had a positive attitude and an anti-Castro essay writer had a negative attitude.  However, when told that the writer wrote pro or anti based on a coin toss rather than personal belief, still on average, more subjects believed that the tone of the article reflected the personal beliefs of the writer.

It is difficult for humans to take situational factors into account.

To counteract this error, deliberately consider other possible sources of influence:

• Personal Motivation: They want to do this
• Personal Ability: They don't know how to do better
• Social Motivation: All their peers want them to do this
• Social Ability: None of the peers are able to help them do better
• Structural Motivation: The organisation rewards them for doing this
• Structural Ability: There is no organisational support to do better.

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This approach, which I prefer, is primarily based on the Crucial Conversations / Crucial Confrontations books but I've seen others use Fierce Conversations and Discussing the Undiscussable.

I also find it useful to understand explanatory style (Learned Optimism) and fixed vs growth mindsets (Mindset).