Or maybe look at the other side of things. What if the guy works midnights and you wake him up when you practice? I KNOW that would piss me off, REGARDLESS if you're playing "technically proficient metal".
How about turning down? Everyone in the neighborhood wins. Neighbor is happy, you still get to practice.
What about when teh neighbor is deliberately calling the cops as an act of revenge?
True story - I live right next door to a house full of off-campus college renters. Parties galore...they use our driveway to cut through, they party loudly until 4 am, etc etc. I called the cops on them one time since asking nicely wasn't helping..now whenever my kids practice guitar and bass in the garage, they call the cops on them for revenge. Calling the cops on a 10 and 14 year old for revenge for us calling on them for a 4 am wild party. Nice huh.

