I mean if there is any chapter that sincerely and seriously needs a solid bitch slapping it is the Space Wolves.
Agreed, the space wolves absolutely must be punished and brought to heel, their flaunting of the imperium's authority has gone on too long. They've proably only evaded sanction so long because all too many inquisitors were distracted by baseless theories about the noble dark angels and their "suspicious, secretive behavior" and "seemingly coordinated actions with their successor chapter" or the "atypically high causality rate of allied forces in thier vicinity".
EDIT: More seriously, though, I think the Sisters earn the top spot for me in terms of my least liked 40k army (that or Dark Eldar, because Dark Eldar are just Chaos marines for edgy people that are into emo music instead of death metal). Largely because their background lore is just so dumb.
The SoBs exist because the Ecclesiarchy briefly took over the entire imperium and proceeded to badly bungle it. In the aftermath, the new Ecclesiarch Sebastian Thor implemented the decree passive, which banned the Ecclesiarchy from ever again having control over "Men at Arms", because Thor determined that they could not be trusted to have military forces and not misuse them.
Then, for some bizzare reason, Thor set about rules-lawyering his way around the decree that he himself had created, setting up the Sisters of Battle as
women under arms and therefor not covered by the decree, recreating the exact problem the decree was meant to prevent. And even more absurdly, that worked (which has hilarious implications for the rest of the setting if that reading of "men = males, not humans" is applied to it).
It also seems more than a little insulting to women, given that SoBs only exist because the Ecclesiarchy can't have the army it really wants and had to make do with women.