In college I used to have to take the bus to campus and my roomie and I would have a competition to see who could start a conversation that would pull in the most people. Being young and slightly full of ourselves undergrads we would always frame our conversations in hoity toity academic language and apply as much scientific theory as possible...but about the most ridiculous topics.
Our most successful one was about zombies and determining the most optimal location to survive an invasion. It included developing a working set of rules for how the zombies infected, functioned, and could be killed as well as population percentages, time of year, etc. etc. Over the course of the 30 minute ride we pulled in 7 strangers into our conversation to add their own bit of expertise in solving the problem.