If you remove the comedy and parody, it would be a nice and tragic story

Jimmy and Mary just kids, Jimmy gives in to his temptations and falls apart.

He tries to rape Mary, but she lets it slide because she really loves him and can't understand what's happening.

Then Jimmy has a conscious crisis fueled by his religious upbringing, and he goes off to see Mary. In his way under the influence of drugs he commits a brutal hit & run and escapes.

Now what would be one of the most touching moments. Jimmy, still under the influence, meets Mary he finds redemption both from Mary and from himself and swears to leave his addiction behind, and it is like all the wrong things he's done are left behind.

There's a stark contrast between Jimmy's crime and rendemption on the same night. Jimmy and Mary are genuine with their feelings, but in this happy moment it is obvious to the audience how naive they are. Even after everything, Jimmy is just a boy and Mary just wants Jimmy. You can feel pity for them and almost believe Jimmy is just a victim, but you know things won't end well.

Jimmy is weak, and quickly goes back to drugs, but this time he was tricked into it. This reinforces Jimmy's position as a victim, even though he isn't one. From this moment everything goes bad.

Jimmy is wasting himself away at the drug den and Mary seeks him. With time Mary goes down the same way as Jimmy and becomes a junkie. Now what would be an interesting moment that would put Mary's character into question.

Her behavior changes completely, she's not a nice girl anymore. Was she repressed by society? Did she want Jimmy because she was expected to? Did she really love Jimmy? After all it is the 30's and women were a lot less independent back then. But did she find release, albeit self-destructive, or was she corrupted by bad influences? This is for the audience to decide, what really matters is that now Mary each day tosses part of her future away.

Now for the tragic moment, Jimmy finds Mary with Ralph, a fight starts, Jack shows up, tries to set the fight apart, Jimmy is knocked unconscious and Jack accidentally shoots Mary. Jimmy wakes up and is led to believe he killed her.

Now Jimmy finds Mary near death, in her arm they remember how much they loved each other and give a genuine display of affection and belief in true love, like shown before, they are after all just kids.

Jimmy is sent to prison and eventually put to death, but not before years of agonizing guilty for a crime he didn't commit.

Of course it would have to be a different drug than weed, and during the movie there should be hints that Jimmy and Mary weren't the perfect innocent kids with a perfect life before falling into drug addiction.