We're happy to clarify (e.g. https://news.ycombinator.com/item?id=13108614) but it's impossible to draw a precise line. Moderation is about a few core principles and a lot of case-by-case judgment calls, and it's inherently unsatisfying.
Whatever rules we have, though, we apply them less rather than more in cases where YC itself or a YC startup is at issue. That's one of the rules :)