He didn't have any amount of aggression towards Hermes. He didn't hate him, didn't have a vendetta against the god, he didn't even particularly dislike his company. He honestly didn't mind that the other had even saved his hide in one occasion. Hermes was simply one of those who he could appreciate in small doses. It was the lack of severity, the fact that the god had so much fun, and when juxtaposed with the wargod, Ares was business and vices, not pranks and Ares was about as fun as a brick--one single brick, nothing else, something that became fun when you threw it at other objects else in hopes of breaking something. He should like Hermes--and perhaps that was really the crux of the issue.
The problem was that Ares did like Hermes, but Ares was unfamiliar with the concept of camaraderie outside of the battlefield. The concept was difficult to grasp for someone who was so accustomed to disliking most things. So, naturally, Ares acted out in a manner of friendliness he knew best.
"You winged dunce, you're no better than some fattened pigeon." Ah, yes, elementary-level insults paired with a mocking tone, this is your feared and mighty god of war. "Have you ruined anyone's day yet, or does that honor go to me?"