There are few absolutely over the top crazy things like the WHFB Greenskins or Skaven had...well, I mean, if a huge walking and facesmashing Whiskeybarrel next to a catapult wich can lob exploding piglets is not crazy enough. ?
If it's not enough, add Gremlin Cavalry on Pigs and roosters for good measure
The perceived crazyness, in my opinions, comes from many little things, like being able to damage your own models to get more Actionpoints (mostly Somer's Crew Box) or getting insane Damage with Dumb Luck, hurting yourself in the process (strong theme in Ophelias Box). Also, both of these rules would play a little bit of the "complete disregard for each other's life" theme you mentioned.
Wong's Box is also filled with crazyness-from absolutely unreliable wizards to a Gremlin Wrestler, it's filled with insanity.
Also, the Brewmaster, especially the Moon Shinobis, who change plusflips to minusflips and the other way round...just imagine a drunken Gremlin, that could win a Fistfight against a huge meeleoriantated enemy henchman, but on the next turn getting wrecked by an enemy Gunman-Minion or something
So, it's difficult to say. There is no "absolutely craziest box" for the gremlins.
But I would suggest Ophelia laCroix- after all, they also have Pere Ravage added to the "regular" gremlin insanity- Pere blows everyone (includin him) to pieces with explosive Pigs