I Like Making People Laugh

A Montana State Trooper was patrolling late at night off the main highway. He sees a couple in a car, with the interior light brightly glowing. He carefully approaches the car to get a closer look.
Then he sees a young man behind the wheel, reading a computer magazine. He immediately notices a young woman in the rearseat, filing her fingernails.

Puzzled by this surprising situation, the trooper walks to the car and gently raps on the driver's window. The young man lowers his window.
'Uh, yes, Officer?'
The trooper asks: 'What are you doing?'
The young man says: 'Well, Officer, I'm reading a magazine...'
Pointing towards the young woman in the back seat the trooper says: 'And her, what is she doing?' The young man shrugs: 'Sir, I believe she's filing her fingernails.'

Now, the trooper is totally confused. A young couple, alone, in a car, at night in a lover's lane ... and nothing obscene is happening! The trooper asks: 'What's your age, young man?'
The young man says: 'I'm 22, sir.'
The trooper asks: 'And her ... what's her age?'
The young man looks at his watch and replies:'She'll be 18 in 11 minutes..'