Our Gemara on amud beis reports that one sage rebuked another for asking him a question about a subject that he was not familiar with, as this causes unnecessary embarrassment.

Rambam (Laws of Sales14:14) codifies this as a form of ona’as devarim hurtful speech. Magid Mishna (ibid) refers to our Gemara as the source.

Sefer Chassidim (972) takes this moral sensitivity even further:

If someone knows himself to be renowned as sharp-minded, he shouldn’t even sit to listen to another’s derasha whom he suspects sees himself as intellectually inferior, for the speaker will see him and be embarrassed.

This is a high degree of sensitivity and respect for another’s feelings.  Let us analyze this principle: Presumably, Sefer Chassidim holds that the junior person will be embarrassed to speak in the presence of the much wiser and renowned sage. This will cause him to be flustered and make errors, leading to even more embarrassment.  This seems to be evident from Sefer Chassidim’s words.  However, Pirush Kadmon (a 17th century commentary on Sefer Chassidim) explains it differently:

He will be embarrassed because the presence of the wiser sage will cause the audience members to gossip and say, “How brazen is this so-called rabbi who thinks he can lecture in front of this great sage?” 

We must ask, why didn't Pirush Kadmon go with the simple explanation? I believe he held that since there was no direct action, and when one gets up to speak, it is, so to speak (sic), at your own risk, the elder sage has no responsibility for what it will cause the younger sage to think or feel.  It is not comparable to our case in the Gemara, because there the person asked a question. He took physical action, when he should have suspected that the question was not within the knowledge base of the person whom he asked. That was a verbal act, and therefore ona’as devarim. However, while perhaps (if I am right) that Pirush Kadmon held that one is not responsible for causing another person’s insecurities without causative action such as speaking, why is Pirush Kadmon’s reason more compelling?  I believe the reason is that in Pirush Kadmon’s scenario, at least a rabbinic form of lifnei iver (causing someone to sin) applies. For example, we have a teaching (Arachin 16a): 

A person should never speak (excessively) about the goodness of another, as through speaking about his goodness it will somehow cause criticism to be spoken as well. 

Rashi gives two reasons: Either he will come to speak about him in a derogatory manner, as he will eventually note the exceptions to his goodness, or his listeners will temper his praise by mentioning that individual’s bad qualities because they will have some kind of jealous or critical response.

When it comes to lifnei iver, the bar may be higher. Thus to even indirectly cause others to say l’shon hara is forbidden, which is known as avak l’shon hara.  This is why Pirush Kadmon forbids attending the lecture, not because the other’s self-esteem issues will be triggered, but because he will cause the listeners to be critical and say l’shon hara. 

I cannot tell for sure if my analysis is correct, but the halachic difference is significant, because it revolves around how much we should have to worry about another person’s triggers.