People think I'm lying when I say I get over 50MPG in my new car… Why?

I bought a new Honda Civic and I often get 50MPG on the highway. I actually got 57MPG on a 70 mile drive but no one believes me? This is a regular Civic and not hybrid.

They all claim I am lying. Why do they think that?
Added (1). Well the trip computer on the car even says 57MPG and when I calculate it manually, it's almost spot on. When I take a photo and show it, they claim it was doctored or something.

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