People chewing with their mouths open, that annoys sometimes. I've confronted some people with it before, and their excuse is that the food tastes better that way. Well that's all fine and dandy but remember other people than yourself have to listen to it, hence why std. etiquette is to chew with your mouth closed. I always chew with my mouth closed, anything else feels unnatural to me to be honest, and I honestly don't believe that my food would taste any better chewing it with an open mouth instead.