How far away can someone be in intelligence from you before you just "don't bother"?
If by intelligence, you mean common sense...
Then, no, I do not like to "mommy" a grown adult.
Otherwise, I would feel offended if the other did not understand my ramblings. Because they are saying that I'm different, and I just want to be normal. I really wished to connect.
I would define intelligence as the ability to communicate clearly.
I don't bother when they throw "responsibility" around like a game. It's a snarky attitude that they have, which repels me... Not expressing their raw feelings; hidden agendas.
Btw [MENTION=27425]Listening[/MENTION] great thread open. =)
Oh, to answer the question final and directly: when they have no interest in mature topics; when they're comfortable in their stupidity.

If they bore.
I usually can swallow irrelevant speech, but there comes a point when I gasp for air.