I read an editorial a while back about people saying "oh my God!" and the writer thought it was very bad. He, being a Christian man, was highly offended. It never occurred to me that it could an objectionable expression. However, the other night I watched an episode of Extreme Makeover - Home Edition that feature a woman from Jamaica who had her house, and her whole neighborhood, renovated. At the end of the show she and her family got to go through the house and marvel at the transformation. They went running through the house and all the said was "oh my God!" over and over again whenever they went into the room for the first time. As I was watching, I thought about editorial I read. I wasn't necessarily offended by her outbursts, but after a few times, I really got tired of hearing it. It began to grate on my nerves so I changed the channel and turned my attention to something else.
My late step-father had his doctorate in English and would often remark that Americans by and large have a very limited vocabulary. He would say that there are so many words in the English language and we use about a tenth of them. Some of them aren't even in the proper dictionary! I think that he blamed the education system mostly, but he also lamented that people are just plain lazy.
It's hard to learn a new word. You have to remember the word, remember how to use the word properly, and then think about when to use that word again. When you write, you can always cheat and use the tools in your word processor to help you find another word in its place. But when you are speaking you have to remember that you already said that would and it's hard to not say it again. In a situation when excitement takes over, you are overwhelmed and your brain can get stuck on the same phrase over and over again. It's easy to become repetitive without realizing it. I suppose if one is more versed in their vocabulary, one might be able to vary one's speech. But in the heat of the moment one finds themselves blurting out the same expletive over and over again without thinking about it.
I often wonder about the origin of language. How did it grow from the simple utterances that the very early humans made? How did the early human realize that they had the ability to form words and decide that "milk", for example, means a white liquid that comes from mammals? I find it fascinating.