ok i may be unpopular for this opinion, but as someone with a brain injury and all the associated mental health issues, i can say, i just think its a non issue, once you stop being able to use humour and stereotypes (and in this case fancy dress can only work on stereotypes - think about it, fancy dress is a parody or a caricature of a stereotype)
anyway once a subject becomes taboo and people are scared to joke about it, incase it offends someone then you are creating a much bigger division between those two people.
we should be celebrating our difference not hiding them under the cloak of an 'ism'
and whilst i agree that taking the piss out a person or people with mental health issues is wrong
its all about CONTEXT
this was a fancy dress costume, most killers and psychos in films have mental health issues, ergo a stereotype is born.
and whilst the rest of the world thinks that stereotyping is bad, i do not, and we all do it in one form or another, just most people wont admit to it, well i do and it helps, especially with a brain injury as it gives me a starting block to start at when i meet people, then my starting point will adapt as i get to know that person, but starting from scratch is much harder so if i talk to someone who has a grumpy face i will assume they are a miserable person due to my stereotype have, and i will tread lightly, because i dont want to be all full on an happy with a grumpy person who is only going to tut and roll their eyes at me (i hope that makes my point)
so in my own opinion more harm has been done than good in this case, because i now looks like those with mental health are now joining the easily offended brigade of all the other ism's
and not only that someone else getting offended on my behalf and the behalf of other people with mental health issues is discrimination in itself.
the world needs to calm down and not get offended at everything, and realise that people say and do stupid things
phew soapbox put away now lol