I think I am a person with a good sense of humor but when it comes to certain things I am very serious. Purim is a joyous holiday and meant to be fun but i think sometimes things are just not funny and pushing it too far. Here are some costumes that I have seen over the years that get me angry. I will start with the one that gets me angry the most.
1- People who dress up like Arabs or Palestinians such as Yassir Arafat, Osama Ben Laden or any other person that would fit into this category. I just don't see the humor in this. Why is this funny? Arafat is a murderer as is Ben Laden. Would someone dress up at Hitler on Purim and walk into a Hungarian Shul in that costume? I don't think so , so why are these costumes acceptable.
2- Yeshivish/Litvish/Misnagdish people who dress like Chassidim. What is funny about that? Are these people jealous that during the year since they dress like goyim on Purim it would be funny to dress like Jews. The way Chassidim dress is funny to them? What about in Shulchan Aruch where is describes how we should wear long coats? Its good to make a joke out of tradition and mock those who want to follow a tradition? Would you ever see a chasid shave his beard on Purim to dress like a misnagid? I don't think so, so why is it ok for them to do?
3- Men dressing like women. I don't find the humor in this. I am pretty sure that halacha does not permit a man to dress in womens clothing as per the Torah and I don't remember seeing an asterisk in the Torah that brings you to the bottom and says excluding Purim. It is especially not funny in America now because people actually cross dress and they are serious about it. Are people who dress like this mocking gays who dress like this? Why is that acceptable.
4- Scary costumes. Many children go to shul on Purim and can get scared of a scary costume. Is it funny and joyous to scare children? I don't think so.
If someone disagrees with me I would love to argue. I could be wrong but I feel pretty strongly about this. There are plenty of happy shatnez free family oriented costumes that are available. If someone is creative they can also create one on there own as well instead of stooping to these levels.