They say there is usually truth in humour.I'd say all of your reasons are valid.I think for most of us the main reason is that this is a very, VERY frustrating business most of the time - for so, so many reasons. For many of us, our sharp tongue (not that we would ever be like this in 'real life' for most of us have no spine and certainly have more sense...) is a way of venting anger and frustration in a way that prevents us going bonkers and flipping out when things don't go our own way.Basically, we're a function of the world in which we live. And this crazy, crazy world results in people saying crazy, crazy things.