It seems that not enough people have received the message that carrying a backpack on public transit, or in any crowded urban setting, is not the same as carrying a backpack on a college campus or, say, to a park. And now that designer backpacks are more popular than ever, especially among the twentysomething set, we here at SFist feel the need to revisit this all-important topic as we kick off another Etiquette Week. (Our sister site in New York covered this growing problem; now it's our turn.) And maybe, just maybe, the most impolite and unaware among you will discover that you've been doing this backpack thing all wrong, and all of our lives will dramatically improve as a result.

Let's get the most important part out of the way first.

DO NOT WEAR YOUR BACKPACK ON YOUR BACK ON A TRAIN, STREETCAR, OR BUS
No matter how crowded or uncrowded the vehicle may seem, your big backpack sticking out from behind you is probably hitting someone else in the back, and it's taking up valuable space that could be filled with other passengers. Kindly take the backpack off while standing on the train platform and carry it in front of your knees. Bumping people with it at knee/shin level is far preferable to bumping them in the face or shoulder when you turn around not thinking about the 30 pound hump on your back. ALSO, there are many crimes of opportunity that happen on crowded Muni/BART vehicles, including cell phone thefts and the like, and if you have anything valuable zippered up back there it is in prime position to be stolen. And you might not even notice when it is.

WHEN MOVING THROUGH A CROWDED VEHICLE, KEEP BACKPACK IN FRONT OF YOU
It bears repeating: Hold the backpack either in front of you, or, preferably, down by your legs, and gingerly maneuver it through the crowd, being sure to say, "Excuse me," and to acknowledge that you have a large piece of luggage that is bumping into others. This is doubly important because you should always be moving toward the center of the car and clustering around doorways, as discussed in our etiquette post of 2012.

KEEP BACKPACK BETWEEN YOUR LEGS WHILE STANDING
Maybe you don't want your backpack touching the floor, in which case holding it in front of your legs is an okay compromise. But really, the best and most polite place to keep the backpack on a crowded vehicle is between one's legs.

STEP OFF THE TRAIN MOMENTARILY TO ALLOW OTHERS OFF
Another rule of etiquette that bears repeating, which is doubly important if you're carrying a backpack: When arriving at a stop during rush hour, and when you are positioned right in the door, do not try to push further in while others are trying to desperately push their way out. Kindly step out of the door and to one side to allow other passengers to squeeze out, thereby making some more room for you to step back in.