Scott Adams keeps talking:
As a general rule, the more dangerous or inappropriate the conversation, the more interesting it is. You'll have to use your judgment to know when you've crossed the line.
Also as a general rule, conversations about how people have or will interact are interesting, and conversations about objects are dull. So steer toward topics that involve human perceptions and feelings, and away from objects and things.
You also want to avoid any topic that falls into the "you had to be there" category. For example, if someone is describing a vacation, avoid asking about the food. Nothing is more boring than a description of food. Ask instead if the person answered email from the beach. That gets to how a person thinks, and how hard it is to release a habit. And it could provide an escape route to move the conversation to yet another place. Sometimes it takes two or three bounces to get someplace of mutual interest.
My thoughts here.