2. Using it to call attention to a double entendre that either you or someone else said, in the same vein as 'that's what she said' (how i've heard it used mostly among my friends)
What you're talking about falls under category 1, which I agree is stereotypical and frankly childish.
But category 2 doesn't come off to me as relying on any stereotype for humor. Only the double entedre.
If in fact it's offensive simply because the words 'no' and 'homo' are in close proximity to each other, than that's a different discussion. I'm just trying to flesh out the context in which it's sometimes used...
I don't understand what you're talking about. You need to give concise conversation example. You mean something like "No kidding?" then why don't just say "No kidding"?