[TRIGGER WARNING - eating sounds]
My mom used to eat hard candy all.the.time. The sound of one of those things rolling around in her mouth clicking against her teeth combined with the sucking and smacking sound of her lips absolutely drove me mad. The fact that my mom is a full blown narcissist that made my childhood a living hell also doesn't help.
So for me it's the combination of the absolutely horrid sounds that are directly linked to the personification of childhood neglect. Whenever I hear those sounds, now 25 years later, they invoke such a strong reaction that I want to punch the person eating in the face.
After thinking about this for quite a while and before I knew misophonia was "a thing" I always felt as if that instant rage was more oriented towards the source (my mom) than towards the "offending person" in present times.