I like this one. Thanks for the reminder:
I have an older brother that does that! He also eats with his elbows out, knife in one hand and fork in the other, like he's on a football team blocking people--but a real defining moment for me in life where I figured out when it was NOT ok to make an issue of the smaller annoying things happened when we were both in gradeschool and he would always slurppppp his cereal with every spoonful as I sat with him at 7:00 am every morning at the table. EVERY SPOONFUL was a slurping noise--this wasn't a one time thing either. So I, being the awesome communicator that I am, got really annoyed for some reason (I guess this is my very first Pet Peeve) and decided to slurrrp too! He told me to stop 3 or 4 times until he got pissed off at me imitating him and then he threw his bowl of cereal all over me. My Mom actually laughed at the absurdity of me being covered in Lucky Charms and milk and took his side ("Brian was making fun of meeeee!") and didn't punish him and made him clean up the mess.
I thought it was interesting life experience. Someone cuts me off in traffic I think of being covered in cereal. Someone butts in front of me in line and I try to think of being covered in cereal and milk. Anything where human interaction can involve someone reacting physically, I think about being covered with cereal and milk in the morning.