My advice would be: Try to get the most out of meeting with them. It's easy to look down on the "soft sciences", but you'll be surprised at the insights you may learn. You should not use jargon, even if it sounds mundane to you, they won't understand it and think you're doing it deliberately to look clever.
Also, I should mention that I am indeed fascinated by the multitude of topics that other have studied, but that I don't know anything of. That's the problem, I believe: I want to get past the mundane "So what is that?" sort of questions.
Edit: It's really the same as holding a conversation with, say, someone who's in a technical profession you don't know about, or a family member you haven't met for a long time. We liberal arts majors aren't aliens!
One example from a topic I worked on: author attribution using stylometry. To a CS (or EE or whatever) the thought that you can take a corpus composed of writings from various authors and train classifiers to differentiate the unique styles of each would be mundane. To some English majors, such a strong structuralist approach would border on sacrilegious (remember Prof. Keating's reaction to such an approach to judge poetry in Dead Port's Society). Each approach has something to be said for it but it has to be done delicately, otherwise polite discussion becomes impossible.
Generally, it's probably better (more polite) to say "I am pretty sure it's actually..." or, "I always thought it was .." even when you know 100%.
Wikileaks is probably a good topic of conversation (politics and technology).