"Hello Ufo" joke

A flying saucer landed at a gas station on a lonely country
road. The two space aliens inside seemed completely unconcerned
about detection; in fact, the letters "UFO" were emblazoned in
big, bold letters on one side of their shiny craft.
As the station owner stood and gawked in silence, paralyzed with
shock, his young, blonde attendant nonchalantly filled up the
tank and then waved to the two aliens as they took off.
"Do you realize what just happened?" the station owner finally
uttered.
"Yeah," said the blonde attendant. "So?"
"Didn't you see the space aliens in that vehicle?!"
"Yeah," repeated the blonde. "So?"
"Didn't you see the letters' UFO' on the side of that vehicle?!"
"Yeah," repeated the blonde attendant. "So?"
"Don't you know what' UFO' means?!"
The blonde attendant rolled her eyes. "Good grief, boss! I've
been working here for five years. Of course I know what' UFO'
means - it means' Unleaded Fuel Only'.