About Men In Black.

I seldom watch movies,so watching men in black made me feel fresh.I found a lot of slangs I know. I was very surprised to find them,because the movie had so many slangs than I expected.I sometimes talk with foreign people,but I have never heard them. I think slangs are very dirty words, so they  seldom use them. However,I wonder why men in black use them pretty a lot,why foreign people I talk with don't use them. The reason why I know them is my friends tell me them a lot. I think it funny, but I think I shouldn't use them because they are very dirty words and mede me less dignity.