I watched it a while ago but I can make a safe bet that it was not before 2000. The protagonist/main actor is a young kid that has never had sex before. He walks around with a trench coat all the time, very sad/depressed, always keeps to himself. I believe one night his dad gives him cash to go out with a girl, but don't quote me on that part. This is most specific scene I remember: I distinctively remember the girl driving (her car) and they were stopped/parked in a lot. She then jumps over from her driver's seat onto his lap (he is in the passenger seat) and she has sex with him for his first time (she was not a virgin). He ejaculates within seconds and she gets off. He then says something like: "It was my first time, I'll get better". I think she takes him home after but I can't remember. When he gets home, he is mad.

I can't remember much else. But the main actor makes me think of either Freddie Highmore, Michael Cera or some small puny kid like that. What are some other young actors that fit that body type?