My neverending struggle with my younger son is to get him to walk in a non-annoying manner on city sidewalks. I'm like a broken record: "Walk in a predictable way. Watch out for other people. Don't swing your arms around or make other sudden movements." He's like a fucking suburban kid!
People with backpacks on the subway are supremely annoying. They love to turn from side to side smacking everyone in a 100 degree arc behind them. It should be legal stomp on their toes, I think, but banning backpacks outright is going too far.