Why does Damon hate stefan?

Answer 1

Damon is not really evil, just very misunderstood.

In the books, both he and Stefan killed each other when they thought Katherine was dead and turned into vampires as they both had her blood in their systems.

In the TV show, they were portrayed in 1864 Mystic Falls as being vampire sympathisers and Stefan suggested talking to their father, so he would stop hunting vampires. Damon told him not to but Stefan went behind his back and it eventually led to Katherine's capture when she injested vervain while having sex with Stefan.

Both brothers were shot dead trying to rescue her and after Stefan forced Damon to feed so he wouldn't die, Damon also became a vampire and later promised his brother 'an eternity of misery'.

After Stefan managed to control his need for human blood, with help from both Damon and Elena, Damon revealed that he still hated his brother as Katherine turned him into a vampire when it was just supposed to be him.

Answer 2

Damon hates Stefan because he's selfish and cares only about Elena. Stefan acts like it's okay to rub Elena in Damon's face and be like "look she's mine and you can't have her so ha! in your face brother!" Stefan basically cares about Elena's friends and Elena and that's it not Damon which is very sad, in my opinion. You're supposed to care and treat family with respect otherwise you'll get treated horrible if you treat them horrible. Not only does Damon hate Stefan because he likes to be jerk and show Elena off in front of his face but he also doesn't care about Damon's feelings and his feelings for Elena. I think somewhere in Season 3 Damon calls Stefan a d*ck. I hope this answered your question and this is just my opinion and don't know for sure if this is true or not.