Without a doubt, Them Crooked Vultures at the Brixton Academy. Just really uncomfortably loud. Worryingly loud. It was a bit of a boring gig as well, I hate to admit.
A few months later, this happened:
https://www.nme.com/news/music/them-crooked-vultures-127446
Following on from all the mentions of Sleep and co, my old band once played a gig with a two-piece band called Agents of The Morai - drums and guitar. The guitarist played through a 50w Matamp and 2 4x12 Marshalls. Our drummer had to leave to throw up outside. It felt like our insides were being scrambled.
Funnily enough, we bumped into that guitar player a couple of years later when he produced our second album. He plays for Conan now.