It's well known that 300 took a number of creative liberties in its visual depictions of characters, and especially that Xerxes looked pretty much nothing like the historical Xerxes. However, movie Xerxes's outfit is very distinctive, with various bangles all over including two large neck rings. While not accurate to Persia, is this outfit based on any real-world culture?
This might be better suited to the Comic Book stack. This is what the real Xerxes looked like:
Based on info from this "Behind The Scenes" video, they used Frank Miller's art and just embellished on it for effect.
You can view in Ruins of Persepolis Xerxes's outfits (below) which have ring and necklace
name of Xerxes I was written in three languages and carved on the entrances, informing everyone that he ordered it to be built
But Xerxes look is inaccurate
physical appearance of Xerxes is also inaccurate-the real Xerxes had a beard and never went near the front line.
I think the multiple rings and chains are more resembled to India tradition
In India, the nose piercing is as much a part of tradition as bangles, a mangalsutra or a bindi.