Miami is definitely the most culturally diverse city I have ever lived in, but somehow, people still manage to judge. During my first year here, the kids used to make fun of me for having a British accent because of my studies in a British school in Madrid. I even got made fun of for my Spanish accent when I spoke Spanish because of the lisp the Spanish have when they speak (compared to many of the local Cubans). In the other countries, I was judged for the people I spent my time with. But in the United States, I was the source, and it felt different.
Not just humor, but the overall tone of your application essay is remarkably important. It's also difficult to get right. When you are asked to write about your accomplishments, those 750 words on how great you are can make you sound like a braggart. Be careful to balance your pride in your achievements with humility and generosity towards others. You also want to avoid sounding like a whiner -- use your essay to show off your skills, not to explain the injustices that lead to your low math score or failure to graduate #1 in your class.