If you want to hear a good one, I think this is it:
The older style BMW motorcycles, with carburetors, had to get some emissions controls installed in order to sell them in the U. S. One of those emission controls was a vapor trapping system. When the motorcycle was parked, and a rather hot day, fuel vapors from the tank were directed to the crankcase via a check valve. Also, the tank would store some vapors in the upper portion of the tank, a separate compartment. This made it impossible to completely fill the tank due to the way the tank was made.
When trying to start the engine on a hot day, all those vapors in the crankcase were then drawn into the airbox. And some of the vapors trapped in the tank were also pulled into the airbox. This made for an overly rich mixture that would not ignite. Crank, crank a bit more, until those vapors were drawn thru the engine and out the exhaust. Finally, the engine would start. Or, you could crack the gas cap to let the vapors escape and then the engine would start normally.
So, those vapors, which the EPA mandated be trapped, eventually ended up in the atmosphere anyway, either thru the exhaust while the engine was being cranked, or when the gas cap was cracked. But, there was a vapor trapping system and the EPA was satisfied. They just did not know the the vapors ended up in the atmosphere anyway.