You'd have to find a way to make it a comfortable situation. Start with the surroundings, find where they're most comfortable. Then kind of work it into the conversation. Keep it light, don't ask direct questions about it. A slight hint at it here or there. Maybe something someone else said that you took the wrong way if you're swapping funny stories.....That's all I can think of.

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"BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Will he offer me his mouth? BOY: Yes. GIRL: Will he offer me his teeth? BOY: Yes. GIRL: Will he offer me his jaws? BOY: Yes. GIRL: Will he offer me his hunger? BOY: Yes. GIRL: Again, will he offer me his hunger? BOY: Yes! GIRL: Yes. BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Yes. BOY: I bet you say that to all the boys!" -Meatloaf