Imagine this situation:
You find yourself at a shuir/speech and you find out that the speaker is someone who has blatantly lied to you on numerous occasions.
You find yourself in this awkward situation of not knowing whether or not you should walk out of the room or just stay-put and listen, just to avoid the drama of people noticing that you're leaving the shuir- something you would never do otherwise- which may get them suspicious and/or vocal about their curiosity.
So you decide to stay-put (to avoid the loshon hara and drama, leaving would ensue) only to find out that the topic of the shuir is about lying.
Throughout the shuir the speaker makes excellent points on why lying is bad and gives excellent examples and explanations on the consequences of lying. But you can't seem to really appreciate the points because you really know the speaker, and you know that everything he's saying is truly hypocritical in your eyes, and taking his words seriously just makes you feel somewhat inept.
During the speech you try not to laugh.
Finally the speech is over and your friend starts going on and on about how amazing the shuir is. What do you say to her?
You can't lie and say "wow the speaker was amazing" because the very reason you didn't like the speech was because of the speaker. But if you say anything (assuming you're talkative) neutral, such as "the content of the speech was excellent" your friend may notice something is off.
What do you do?