Don't be caught doing any of these things…with your left hand.
At the dining table, pass to the right
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Good dining table etiquette requires passing food and drink to the right. This rule is an attempt to impose order on the process of passing food and drink at the dining table. "What's important is that when several dishes are being passed at the same time, they all go in the same direction," Emily Post explains. In other words, the rule could just as easily have been "pass to the left." But someone chose "right," and so it is.
Open the doors on the left-hand side of your car
Using your left hand to open any of the car doors on the left-hand side of your car increases the risk of "dooring" accidents (where a bicycle rider coming up alongside of the car gets hit by an opening car door). If you open the door with your right hand, you're forced to pivot toward the left side of the car, which means you're more likely to see a bicycle coming up on your left. This method of door-opening is named for one particular country, which pioneered it. Can you guess which one?
Using your iPhone to talk on the phone
"If you've got an iPhone, you're likely to get better reception if you hold it in your right hand (and right ear) during a call," according to a report commissioned by the Nordic Council of Ministers regarding how effectively different smartphones caught and sent radio signals. "This could be because the left-left combination adds a greater obstruction between the phone's antenna and the wireless signal than a right-right combination would," suggests Quartz, a business thought leadership publication in its post about the report.
11 Things You Should Never Do with Your Left Hand, Source:https://www.rd.com/culture/things-never-do-with-left-hand/