"...chimps also bare their teeth when they are frightened, uncertain, or uncomfortable" And so do we - and, as has been pointed out in this thread, it is when we are frightened, uncertain or uncomfortable that we are liable to get violent. But sometimes we can use humour and laughter to help pull us through.

It's maybe a shame that our closest relatives are chimps, rather than orang-utans or gorillas, who seem to have less volatile temperaments, from what I've heard.