I've watched Stand by Me at least 100 times since my early childhood, and on a recent rewatch I noticed something in the film that gave me an answer to a question I've always wondered: Why does Gordie Lachance take aim on Ace? And further more, when Ace asks Gordie - "What are you gonna do, shoot us all?" Why does Gordie respond - "No Ace, just you."
From my perspective it had always seemed as if Gordie had a personal vendetta against Ace, beyond the bullying and threats Ace makes upon Gordie and his friends. So. What is this personal vendetta? Ace killed Gordie's older brother, Denny.
Here's my evidence. And It might seem thin, but there are just the perfect amount of clues to lead any viewer with a keen eye to this conclusion. In the beginning of the film, we learn that Denny was killed in a car accident. There are no further explanations here - when, how, or where. Here's the exact line -
"In April, my older brother Dennis had been killed in a Jeep accident. Four months had past, but my parent's still hadn't been able to put the pieces back together again."
Later in the film with Ace's gang, two of the most (imo) memorable and significant scenes are where they are playing baseball with the mailboxes and playing chicken on the road. Ace completely runs the truck hauling lumber off of the road and cuts off the driver he was racing.
My theory here, is that Denny got into a similar situation with Ace. Ace running Denny off of the road was the cause of his "Jeep accident", but his family doesn't know. And I think Gordie either found this out somehow, through small town rumors, or just simply knows instinctually - just as us as the viewers might assume from watching these same scenes - that Ace played a significant roll in Denny's death.
For me, this revelation changes the meaning of the confrontation scene between Gordie and his friends and Ace's gang. Because now not only is Gordie standing up for himself and his friends, but he's standing up to the guy that killed his brother, redeeming his brother's death by threatening to kill Ace. There's even a little exchange of dialog between Ace and Gordie before Gordie cocks the gun, that hints back to this theory.
Gordie - "I'll kill you I swear to god."
Ace - "Come on Lachance, give me the gun. You must have at least some of your brother's good sense."