I don't know when it happened, but my sister now chews with her mouth wide open. I wouldn't notice it as much but she makes this atrocious sound when she does it. It happens when she eats any food... cookies, dinner, whatever. The sound she makes whenever she chews just completely grosses me out. She also makes the same sound when she chews on her fingernails. I wouldn't care about that either, but it gets to me.
Is there a way to tell her not to chew with her mouth open without completely offending her? Whenever my mom tells her not to chew her fingernails, she pretty much freaks out, so I'm sort of hesitant in saying something. Not only does it bother me, but apparently someone at college pointed out how she chew with her mouth open, and she got hurt by it. I want to tell her that if she only closed her mouth, people wouldn't notice. I feel like if she doesn't stop now, then she never will, and she'll end up chewing with her mouth open at some important dinner, or during a business lunch, or something like that. My parents stress learning good manners for occasions like this, so I feel like I should tell her. Or, am I being a dick by pointing this out?