Eddie offers Beaver a ride in his new car. Beaver gets in the car, and then says he can't go right now. Eddie is ticked and storms off.

Why would Beaver get in the car if he couldn't go right now?

I don't remember the episode exactly, but didn't Beaver get in the car, then suddenly remember that he had to go somewhere else?

Eddie offers Beaver a ride in his new car. Beaver gets in the car, and then says he can't go right now. Eddie is ticked and storms off.

Why would Beaver get in the car if he couldn't go right now?

Beaver was probably shocked that Eddie was asking him that he forgot he had plans.

That's probably right. He forgot he had plans cuz Eddie was being nice.