I absolutely hate it when people eat with their mouths open. It's so disgusting. And it's not really the whole chewed up food thing [My dad and brother would always chew their food up and show it to me when I was younger, so now I'm immune to it.] I think it's just the noise. Is it really that hard to chew with your mouth closed? I don't want to hear you chowing down on some chips or sandwich or whatever. The sound of someone's lips smacking or their teeth grinding down some food makes me want to puke. One of my friends eats like that, I can hear her crunching the food between her teeth. It's all I can do to keep from tearing my hair out. My brother does it too, even though he's constantly reminded not to. Thankfully, I rarely eat with him, so that's okay.