Involuntarily making obscene or inappropriate utterances and remarks. It has been described as parrot like or repetitious in nature and it can be traced back to childhood. Some signs of a child that may develop this issue are tics, grunting/groaning noises and shouting as well as compulsive movements of the arms. It can be, but is not always, a characteristic of Tourette syndrome. It can also (upon rare occasion) be a sign of schizophrenia.
You can find a much more detailed explanation of coprolalia here: http://www.medterms.com/script/main/art.asp?articlekey=12349