Oka so Sam started masturbating in the impala young. John would be driving them and Sam and Dean would be in the backseat. Sam would sleep on Dean and like either rut on the seat or stick his hand in his pants and grind on it. Sam always that that Dean didn’t know but he did. So Sam is older now, around 16 I think and he gets injured and John reluctantly lets him sleep on Dean in the backseat and Sam does the masturbation thing and I think Dean decides to like whisper to him or something. I also remember that I think Dean would sometimes run his hand through Sam’s hair and that would help Sam get off but he didn’t know that Dean was doing it on purpose.