I agree it's sometimes a choice to live with the chewing noise, or find someone else. It's not that I care about every little thing. Though sometimes, I have a big problem being assertive because of my past environments making it scary to be assertive sometimes.
I'm most confused when it's related to personal triggers or baggage or difficulties. I need to assert myself early on, but feel bad about doing so. I don't want to spoil the nice new NRE by being so serious. And I seem strange and it's personal sharing these things. However I find over and over, if I don't say something, pretty early, I'll just doom the relationship. When I do try and say something, they usually don't take it seriously enough (because they are in NRE or because I'm trying to make it lighter, less serious).