In my quest for all gold guns, my last two to level up are the KSG and Spas. I have heard comments about my use of all of them, with the least hate coming in for the Model 1887. I think that is because most people have tried the Model out and find it hard to hate someone who handicaps themselves with that POS. I say that out of hate and love for that gun.
My most recent gold shottie, the AA12 has started to rack up a lot of haters. Once you have range and extended mags on it, you can wreck teams on maps like Seatown. Nothing brings out the hate like the "no-skill" auto shotgun. I just thank them and encourage them to try them for themselves to see how they do. Until you get range on it you can't kill much past knife lunge range, afterwards you are good for most rooms and short hallways.
To answer the OP, people hate the OHK (as has been pointed out), I know when I rage, it's when I die without a chance to fight back. If it is against Snipers and Shotguns, you know that unless the opponent is very good, you can usually counter with superior weapons. If it is MK14s/Type 95s, you need to pull on your try-hard underwear.
