A few years back someone got fired from our hospital for showing up with a baby doll protruding from their skirt, á la spontaneous abortion. This year I had to threaten one of my employees with unpaid suspension if he did as he was threatening to do, and showed up in a grim reaper outfit.
We work in a HOSPITAL, for Chrissakes.
October 2001 I saw someone dressed as an airline pilot with a slashed throat and his friend was a “terrorist” with a fake box cutter. I thought it was pretty funny, but no one else did.
How curious – I first saw that as a cartoon in an ancient Hustler … Do you think they would have stooped so low as to rip off Playboy? 
OK, I just got an email from some friends who had a halloween party last night (that way, everyone could go out tonight and tomorrow to the bars and bigger parties,) and in the email was a picture of my Jewish friend, dressed as Hitler, being pushed into an oven.
There was once a costume party where everyone had to come dressed as an emotion… all blue for the blues, green with envy, etc.- not a lot of room to really get creative, except for one guy who was totally naked excpet for a dish of pudding strapped to his waist, with his penis is the pudding. He was…fucking disgusted!
A few years back, a friend went as Jesus Fucking Christ. He dressed as Jesus, and had a blow-up doll attached at the front.
Okay. This is one that most people won’t get, but if you lived in Alaska in the mid-1990s you might.
On Halloween of '94, I saw a guy dressed as Alaskan Independence Party founder/leader Joe Vogler. He was wrapped in a blue tarp, with duct tape.
I went as anthrax that year! I marked a t-shirt to look like a letter addressed to Tom Daschle and covered myself in baby powder.
One of my college roommates went as Courtney Love one year, complete with bloody Frances Bean hanging by an umbilical cord.
Several years ago, at the Stonewall DFL Halloween Party/political Fundraiser, we had 2 people come costumed as a white plantation owner and his black slave boy. We had several people at the party who got very offended, and said that we should have refunded their advance tickets and refused them entrance to the party.
Interestingly, it was all white people, mostly women, who complained about this. The black people at the party made no complaints. (Though late in the evening, after several beers, one did drag the guy in the Abe Lincoln costume over, to free the ‘slave boy’.)
A (male) friend of mine went in a bridal gown and tiara with a big steering wheel protruding out his back, and a sign on his front saying “Princess Die.”
A cousin of mine took the kids trick or treating and they made stop at the local nursing home, which sponsored ToT there to make the residents feel like part of the community.
My cousin was also dressed up. He entered a room and the woman just shouted
“Jesus, take me home now!”
My cousin had to remove his Darth Vader mask to get her to calm down.
It wasn’t until I realized you were from the British Isles that I figured this one out 
Daniel
All the JonBenet costumes are in poor taste. I think the ones showing her after death are the worst.
I don’t know if anyone was offended but I saw someone in full surgical scrubs with a set of stirrups attached to his shoulders. There was a sign around his neck, “Trust me, I’m a doctor”.
A couple of years ago I saw one that seemed to be going out of its way to be offensive – a white person, dressed up in scuzzy clothes with tufts of cotton pinned to it. They had black makeup on. It was obviously supposed to be a black slave. Tied around their neck was a hangman’s noose.
If I may ask, what makes them more offensive than dressing up as a generic dead person, which lots of people do and no one finds offensive?
Aside from the fact that a dead little girl is considered more tragic than a dead adult, it’s always more powerful when someone you know has been killed. Obviously, most people did not know JonBenet, but the sensationalistic media has a way of personalizing public figures, especially murder victims. This is my take on it, anyway. The image of JonBenet has been shoved in our face so much that it’s been personalized for a lot of people - they see their own daughters in it.