Frank Kogan

3) Expressing humor, which may not reflect the speaker's feeling towards the listener at at all.

As you said, people over twenty have usually gone through social conditioning about the harshness of the word "hate," and so don't use it as a straightforward sincere statement except as a last resort to elicit the maximum emotional impact.

But "I hate you" as a sarcastic response to anything can happen in any sort of casual situation, between two people who may not have any sort like or dislike for each other at all, but are merely going with conversation flow, "I hate you" being the punchline of that discussion thread.