My character is now very upset at another character. What are strategies I can use to balance "My Guy Syndrome" with genuine disappointment?
For some backstory. In this particular game we're a bunch of level 1's and 2's. I am a Half-Elf Druid that worships nature and very much cares about animals. Another player is an Elf Ranger. Despite my in game pleas to him to not do this he bought a War Mastiff. I told him I can't condone him buying a dog explicitly for the point of fighting, shackling it in a metal collar, and forcing it into harm's way. He ignored this and I let it go because I know he gets to play his character how he wants to.
He then literally threw the dog over a 10ft wall at some Orcs. The dog promptly died. He then left the corpse behind. I stayed back and am going to properly tend to the dog's corpse. Needless to say my character is very upset. Meanwhile the other player already plans to purchase another Mastiff.
The question is, how can I balance and show this hostility without falling into MGS? I know he deserves to play his character how he wants to just like I do. How far is it appropriate to push animosity between the two PCs? I have a few ideas on ways to treat and interact with the other PC going forward but am hesitant to upset the group dynamics.
I think this is fairly independent of version and possibly even game but if it makes a difference this is Advanced Dungeons and Dragons 1st Edition.