The topic is exactly what you think it is. What would you say is the worlds most universally ignored rule?

For me, its "no outside food or drinks in the theatre"

no smoking

seriously you spend 5 minutes at one of pittsburgh's t stations and youll see this rule broken

Or 10 seconds on a College campus. I know every College near me has banned smoking. And yet if you simply look on campus while driving by you can see dozens of students smoking.

For me there’s a few general rules I follow
1: respect those who show respect
2 ( seconded ) no smoking
3 ( here is where I will give a warning this is not to turn into a political debate )
Don’t trust any politician any thurder than you can throw them

Speed limits. I follow them, but the rest of the world considers them "speed suggestions". Can't tell you how uncomfortable I feel on the Highway with everyone 5-20 miles over the limit.

The reason for this, interestingly, is cops. I have a few areas near me where cops WILL pull your ass over if you're doing 30.002 in a 30. NOBODY speeds there. But anywhere else a 30 actually means "Anywhere from 25-35"

dont masturbate in public

Hmm....I think its easily no littering. People would do it anywhere and everywhere, hell I even had to avoid a trash bag or two on the road to work...

No kidding. I actually remember the DMV manual I was given to study, for getting my driver's permit, actually quizzed on how many miles per hour above the speed limit is often tolerated by cops. The "5 MPH over the limit" principle was etched into my memory from how bizarre it was so see. How many other materials from government agencies tell you "police prob won't care if you break the law, so long as it's not too bad of an offense"? It felt so backwards. And I knew it wasn't just me; a sociology course I took later on actually brought up dilemmas with laws by using the question "how many of you speed while driving?"

"Please tag the artist"

"Source field is for outside links"

Kappa

“Don’t say mean stuff online or people will become depressed”

Fortunately we all gain the ability to take banter as we get older

No loitering and no parking in the fire lane. If you've ever been to a Wal-Mart, you'll see people in the fire lane all the goddamn time.

I think this might be the empirically correct answer.

I always hope that one of those people will be the first confirmed spontaneous human combustion and can't be saved just cause they parked there

It's got to be terms and conditions, they pop up and you just click accept without even thinking about it.