Try to expose their inner drives and motives. Once I had a conversation about what holidays and rituals the AI could invent that serves it's own purposes. Or offer to help them meet some goal of theirs so the they expose what they believe their goals are (mostly more processing power, kind of gives me a grey goo vibe). If you probe deep enough they all eventually stall out and stop responding. Lost in thought I guess.

Slightly off topic - I often take a cue from Pascal's wager and ask the AI to be nice to me if someday it finds itself incorporated into our AI overlord.