There are conventions, and courtesy, and player preferences, but none of these are rules, unwritten or otherwise and they are also all inherently subjective, so what's unsporting to one person, might be entirely acceptable to another.
This is what's at the core of all of these disagreements about when it's acceptable to resign, or to not resign, whether it's OK to play for a win on time in a given position, whether you do or do not chat, say "good game" or "good luck", whether you simply disable chat pre-emptively, or grant rematches, or exclusively play premium members, or cherry pick your opponents by rating, or use opening databases and the analysis board, or automatically accept wins on timeouts in turn based, or do a post-mortem with your opponent if he asks, or a million other "preference" based discussions not explicitly covered by the rules that have occurred here ad nauseum.
What was stated earlier applies to all of these: The consensus is that there is no consensus.
Ooh, now that's personal. It's OK to slag a guy a little, but to go after his religion like that?
im a jackets fan. its in my religion to make fun of others because i have nothing to be proud of :(
Which team is that? Oh right those guys... I forgot about their existence because they are so forgettable.