Despicable Me theory: Mel & DM4 Jerry's friendship
I've already discussed this on Discord but I decided to also talk about it here:
When watching DM4, I noticed something interesting about Mel's relationship with Jerry. As we know, Mel is very friendly now, implying he actively worked on changing his attitude between the events of DM3 and DM4. However, we could also see how Jerry's interactions with him change throughout the 4th movie:
At first, when they're chosen to become testing subjects, Jerry stands next to Dave on the right, while Mel is next to Tim on the left (it's the opposite from our perspective).
Then, during lunch time when Tim uses Jerry to stop the laser, Mel approaches Jerry only to be shooed away.
Then, when the Mega Minions are sent outside for training, Mel shows excitement, gently punching Jerry's arm - Jerry doesn't actively show his anger, he simply glares at Mel with disagreement, not sharing the same positive emotions.
However, when Mega Minions get scared, it's Mel who gives the others courage and during that, he specifically points at Jerry, who’s surprised at first, but then he finally smiles at his one-eyed colleague and from this moment, these two cyclopes are shown to stand/sit next to each other in almost every scene.
Both Mel and Jerry watch Dave jumping to the action to help somebody. Then, in the AVL vehicle after failing the training, Mel and Jerry are (again) next to each other, sitting this time. After defeating Maxime, Jerry is, surprise-surprise, standing beside Mel. And finally, during Gru & Maxime's performance in the AVL's prison, Mel and Jerry are in the crowd and together again - this time, Mel is on Jerry who's rolling like a big ball.
Any theories why Jerry was so unfriendly and rough to Mel?
Mine is that Jerry was mad at Mel for what he has done in DM3 and needed time both to see Mel truly changed for the better and to forgive him.