Handshake
It only takes seconds and is the standard greeting, deal-sealer, and act of forgiveness. But in the good ol’ Roman days, the handshake extended to the elbow and was a way for two parties to check if the other had a weapon hidden under their sleeve. It wasn’t until medieval Europeans that we started to clasp hands and shake, mostly to see if any smaller weapons would fall out. The reason we usually use our right hand? Well, the left hand was commonly used as a way to clean one’s self after sitting on the toilet. Thank you hand sanitiser, thank you so much.
Yawning/sneezing
Ever wonder why we cover our mouths during yawns /sneezes and say “God bless you”? In medieval Europe, the bubonic plague spread like wildfire and covering one’s mouth during a sneeze was not only proper, but necessary to help limit the spread of the disease. The saying began when Pope Gregory instructed people to start blessing all who sneezed. Covering our mouths during a yawn was very different in the Muslim and Indian worlds: people believed that a yawn invited satanic spirits into the body and covering your mouth was a surefire way to block it.
Driving on the left, then right side of the road
Again, we look back to Rome as the forefather of left hand driving. The reason? It was easier to kill passersby that were hostile or threatening your life. Most people during that time were right-handed and it was easier to whip out your dagger/sword/trident on your right. The reason for the switch back to the right-side? Guns. Horseback riders would hide their firearms on their left hand side and could easily steer with their right. The right-side change was further solidified by Napoleon and Adolf Hitler who preferred to use the right-side of the road for this reason.