Fill your tank as quickly as possible turns some of the gas into vapor. All pump hoses are equipped with a vapor return that sucks vapor back into the holding tank. That means you’re charged for the gas that comes out, it vaporizes, and never actually enters your car, meaning you get less gas than you’ve paid for.
That loss, though possibly correct on a minute scale, is so insignificant in any practical way it’s not worth considering. Gasoline vaporizes at 144 deg C. Increasing the surface exposure to air at normal ambient temperature when pouring it into a gas tank will make virtually zero difference. The fact that the air in your tank is already saturated and likely at, or close to 100% of it’s absorption capacity makes that doubly so. The pump nozzle’s vapor scavenging action is simply removing the displaced air in your tank so it doesn’t contaminate the air we breathe.
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