Genius level conversation:
Me: Real numbers desk, how can I help you?
Other Guy: Hi, yes. Um, what's 1/0?
Me: Um, undefined.
OG: Yes, but what is it?
Me: UNDEFINED. It's insolvable.
OG: Oh. But, um, if you could solve it, what would it be.
Me: Dude, no: it's undefined.
OG: What about 1/(1-1)?
OG: All right, then, I have one other question. What is the square root of -1?
Emended for Daniel PickyPants.