Japanese's way of talking and vague vocabulary

Last week, we talked about 社交辞令　and 曖昧な日本語　which are two unique ways of talking. If we look from these two forms, we will see that Japanese use various way of communication. They will try to read the situation first and then pick the way. That is interesting. These also express Japanese's way of thinking and treating people. They have to be polite as much as they can when they meet strangers, although they are Japanese. Because they don't know about their background much, so they try not to make any mistakes. I think it is a good idea to do if they talk with Japanese people the same as they are. They should be careful when they talk with the foreigners, since the foreigners might not be able to comprehend this culture.
Apart from the thing I said above, Japanese has lot of words which are difficult to understand and use, for example,　結構　which we saw from the Japanese TV program last week in the class. There might be another Japanese ambiguous words that we should talk about. One word I want to know about is 全然. Before I came to Japan, I studied that 全然　mean not at all and will be used only in negative sentence. After I lived here for a while, I learn that it can be used in positive sentence too like 全然大丈夫　which mean it is okay. In my point of view, some words can be practically used in another meaning although their literally meaning does not mean
like that. It quite surprised me ,because Thai language does not have some kind of these words, so I think maybe we can talk about this.