User blog comment:IamJakuhoRaikoben/Chapter 489: Universe One, Review./@comment-25111584-20160615073844/@comment-25111584-20160615082038

Considering Zeref's earlier declaration of never deciding what to actually do with Acnologia (despite creating an Empire to take him down), I doubt the two have fought before.

And, seeing how Acnologia seems to be portrayed as battle-crazed, wouldn't a strong opponent who won't die be perfect for him? Y'know, knock him around a bit, allow him time to recover, then rinse and repeat. I see Acnologia welcoming the challenge rather than getting frustrated by it. I mean, the guy wasn't even frustrated by Igneel's appearance despite the fact that he believed all Dragons dead.

And, while Acnologia is definitely arrogant, I don't see him trash-talking. Especially since he doesn't really respect humans enough to have more than the simplest interactions with them.