Loki was the sort of god that didn't much care about his people's reputation, he wasn't the pushy parent sort of god who'd go around boasting at everything they'd achieved, he had far more interesting things to do. He didn't care what his worshippers got up to - well, not in a general sense, he wasn't the sort of god who thought it reflected on him, that it was something to boast about, unless of course it would annoy someone else.
Sure, maybe it would have been nice to be able to one-up Apollo about something he actually cared about, and admittedly he quite liked a lot of the artistic things the vikings did, even if they were much more well known for the slightly more barbaric practices - which, by the way, he was also totally fine with - but even if he did find a way to top what Apollo had been saying, that would prove that the other god had hit upon something, or that he'd made a valid point, and Loki preferred to pretend that nothing the other god was saying had any relevence to, well, anything.
So instead of talking about the carvings and culture and poems and epics, and the exploring and the new worlds, he just rolled his eyes.
"Oh, sorry, am I supposed to care that the vikings were too busy doing something to sit around in the sun and paint pretty pictures?" he scoffed, dismissing years of Greek culture in a single, disparaging sentence.
"Hitting things is a test of character?" he repeated with a laugh "Well, sure, if your brains are in your biceps maybe." He ignored the comment about his brother. Stupid Thor.
How could he be so dismissive of everything his people had achieved?! He could understand why he wouldn’t defend his own race of people. They were idiots. But to pay so little attention to the Greeks it was, it was, insulting! Which of course the other god had done several times this very meeting but this, this got him absolutely furious.
“IT’S MORE THAN PRETTY PICTURES! We at least have a system of government never mind a completely fair and democratic one! You and your peoples ideas of Justice was running around hitting each other on the head! BARBARIANS!”
"So, wait, I'm getting confused here," Loki asked with a fakely innocent smile "is hitting people barbaric, or a test of character? Maybe it's you who's getting confused, since you can't seem to decide, maybe it's one too many blows to the head... or maybe you're just a moron, there's always that option."
Loki was fine with the way things worked amongst the vikings, no matter what Apollo decided to call it, it worked for them and who cared what anyone else thought? Plus it was difficult to be offended when he was getting in so many hits - for Loki, an argument was very much like a fight, it didn't matter so much what hits you took as long as you made more. He was definitely winning this fight, if Apollo's rage was anything to go by.