What is your worst pest peeve, Reddit?

Most annoying thing a person can do, and it would be nice to hear a story on how it happened and why it annoys you.

An example which just happened tonight for me. I was out with my mom and sister getting food when Darius Rucker came on the radio singing "Wagon Wheel." I had my headphones, when i hear my sister say, "This is such a good song by him." I proceeded to somewhat get angry and reply, "You mean by Old Crow Medicine Show, right?" And we had an argument about what she said and so on.

TL;DR Cover of Wagon Wheel by Old Crow Medicine Show came on radio, Sister said it was Darius Rucker. HUGE ARGUMENT.