Enter Brax's shop with Radiant Aura on. Blobby comes in and whacks me next to Brax. Aura explodes. BRAX IS ENRAGED. YOU TAKE 20,000 DAMAGE (due to your wonderfully powerful Floor 1 armor). YOU BE VERY DEAD. How...I...what...where...when...UH!?! I have never laughed so hard at a stupid twist of fickle fate.
I once got swarmed under by Dread Collectors because I drank a Radiant Potion while selling to Brax. He took like 2 damage but that was all she wrote for our poor, eyebrowed adventurer.
I stole from floor one, and brax got angry. I proceeded to escape and keep my nearly worthless item because I didn't get a lucky item from 7 floors above in any of my floor one shops. I wanted to steal from every floor on this level but I find nothing good. All I got from level 2 (and this time he didn't notice) was a crappy ring. I don't die from brax, I steal from him, legit. Like a real man (though I was actually on DM not GR). The only reason that happened though is because I rushed burglary to max on that character. Then I went back to floor one, plotted my escape route for the ultimate heist of a cheap useless item, where I probably lost more in the few potions I used, and stole it. Was pretty awesome. I can't go to floor 1 any more though, because he still hates me. But yes one time I did accidentally hit brax with a spell, but I fail to recall what. All I remember is hitting him and getting one-shotted really quickly.
The following is a true story. I often steal from Brax using the staircase trick in order to smooth the drudgery of playing through the first few levels for the umpteenth time by having some slightly more high-powered gear. Naturally, before entering a shop, I leave all my ill-gotten goods outside lest Brax detect my foul play (which he has been known to do on occasion, even on new dungeon levels, leading to a grisly death). One day, I entered a shop on Level 4, looked around, and found nothing of interest. But as I moved to leave, I saw Brax blocking the entrance. "Oh, crap!" I silently exclaimed. For you see, gentle reader, though I had removed all the mighty stolen artefacts I had been wearing, I'd forgotten about the spare Doubleplus Crossbow in my inventory, which I had stolen from Brax on Level 1 and proceeded to enchant until it had the offensive power of a small trebuchet (complete with a chance of raining rocks down upon my enemies). There was only one thing for it. I'd made good use of my Necronomiconomics degree since entering the dungeon, and now it gave me an idea. I was going to try to bluff Brax. "But you see, this cannot possibly be the crossbow you're looking for. That was an ordinary item, rather plain if I may say so, whereas this one is a heavily enchanted artefact worthy of the great crossbow-wielders of Yore. And, as everyone knows, for tax reasons demons only sell bonus enchantments on rings and amulets, never on weapons." Brax hesitated for a second. He knew that I had somehow cheated him, but he also knew that he wasn't going to be able to prove it. So he decided on a what appeared to be a compromise that would allow both of us to save face. "That'll be 0 zorkmids. You have 6371 zorkmids. You want it or don'tcha?" I silently sighed with relief. That had been a close one. I happily decided to pay the symbolic price. Brax's grin widened as he stared at my empty outstretched hand. "You don't have the money, punk!" I froze. "B-But... that's 0 zorkmids. How else am I meant to pay them!?" Brax's expression did not change. "That'll be 0 zorkmids. You have 6371 zorkmids. You want it or don'tcha?" "Yes, yes I want it! Just take the 0 zorkmids already!" "You don't have the money, punk!" Brax cheerfully repeated. "Tell you what," I replied, getting desperate. "I'll buy it from you at full price. How's that?" "That'll be 0 zorkmids. You have 6371 zorkmids. You want it or don'tcha?" Brax's smile was very cold. "All right, I give up. Take the damn thing. I didn't want it anyway!" I shouted. Brax gazed at me dispassionately. "Quit wavin' that thing at me. You gonna buy it or aincha?" I tried every possible conversational gambit, every financial stratagem and cunning trick. But Brax was not fooled. Time after time, as minutes turned into hours and into days, as sanity drained away and hope turned into despair, he had only one thing to say to me. "That'll be 0 zorkmids. You have 6371 zorkmids. You want it or don'tcha?"
That's Karma for you, Vel. And Brax only hates me when I go out of my way to screw with him. Heck, he even lets me try out the merchandise on any creature hapless enough to wander into the store! Though, there was that one time when I took Promethean magic, and I accidentally singed him while taking out a measly Diggle. Wasn't pretty.
The first time I accidentally attacked Brax and got killed by him, it was embarassing. The fifth was the time I decided from now on I wasn't always going to play with permadeath. And then came one sweet, sweet day where, somehow a shove attack with an area of affect attacked him. And this time I wasn't level 4 or 5. This time I'd maxed, leylines, master of magic and almost all psionics too. He couldn't even get within 3 squares of me. I was so giddy when I killed him I actually cackled outloud and announced "now I have the power!" but mercifully no one was within earshot. I decided to be nice and mindshove his corpse and all his gore into a corner before looting anything and dealing with the angry red bouncer demons outside. I liked their shade of red so I tried to use them to paint the walls. Highly recommend it.
Oddly, I generally restart from my last save if I kill Brax, since I keep thinking it'll pull a Spelunky on me and make it so I can't sell stuff to shops. That'd be a big NOOOOO for me there.