Looking for Halloween costume ideas for adults and children? Here are some popular costumes and idea starters. Some people like to blend in or try to have the best Harley Quinn costume and others want to set themselves apart and try to be the only person at a party with their costume. If you’re trying to set yourself apart, the 6 costumes are likely going to be a big fat no for you. If that’s the case, at least you’ll know what to avoid.