"I wanna stay!" joke

A guy took a blonde out on a date. Eventually they ended up parked at a "lovers point" where they started making out. After things started getting pretty good, he thought he might get lucky, so he asked her,
"Do you want to get into the back seat?"
"NO!" she answered.
Okay, he thought, may be she's not ready yet.
Now he has her shirt and skirt off, the windows are steamed, and things are getting really hot, so he asks again,
"Do you want to get into the back seat?"
"NO!" she answers again.
Now he has her bra off, they're both very sweaty, and she even has his pants unzipped. Okay, he thinks, she HAS to want it now.
"Do you want to get into the back seat NOW?" he asks again.
"NO!" she answers yet again.
Frustrated, he demands, "Well, why not!"
"Because I want to stay up here with you!"