Sorry for the long post but the question is complex, so I have answered according to various aspects.
The Bible is pretty clear about using 'foul' language, but what is 'foul' is not always clear. However since the bible endorses brotherly love, if words that you feel free to say at home, offends someone at work, or church, then they should be said at home only.
Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving. (NIV Ephesians 5:4)
The new testament is never legalistic, so it expects each person to apply a verse like this and there is no need for others to define in great detail what it means by actually listing the words. Regarding Carlins 7 cuss words (I had to look that up) even most non-Christians would define most of them as obscenities. Basically, if a teacher in a high school could get into trouble for saying a certain word every day in their regular teaching, it is probably viewed as an obscenity by a large population.
But all humor aside, I think the key idea with obscenity is that it offends. Even if the Bible did not say, do not use offensive language, it is already given that we should do our utmost not to offend our brother. Obscenities are just those words, not evil in themselves, that are generally understood as offensive. Of course many words lay on the border of offensive or non. I am often surprise that some words I use, are considered offensive by some people at my own church.
What makes a word offensive? I think what happens is when we are bitter or angry in a sinful 'cursing' sense we tend to refer to certain word to express our wicked curse. Although the words themselves could be said by a child without any anger at all, the frequency of their use as a continuer for wicked cursing, by wicked men, eventually bring about a strong cultural opposing to the word itself. It is these word which would make our talk unwholesome and unloving.
Now as we approach sin, or things we can hate, while being a loving Christian, we are naturally wanting to use words that properly express our disgust. These are the types of words that Jesus and thenApostle used. Non of these words were considered offensive, but being called by them, would obviously offend, but in a good way. For example sinner is not a offensive word, but many would be offended if you came up to them and said, 'Hi, did you know you are are a wicked, blaspheming, sinner?'
So the only question remaining is when can we use words that although not offensive in themselves, are greatly offensive to those we use them? I think this is something each person must decide according to their faith and proper evaluation of their own attitudes. For example, at home I would say very sharp words about a certain Christian group. I would say they are mostly all deceived. Their leader is a devil. They have always been filthy blasphemes who hate Christians, etc. I would say that to my wife as she would not be offended. At my church I would not say these things so sharply, as I may offend. At work I would not say them as it may be considered as harassment and even worth being disciplined. I would not say these things on this website as it violates the purpose of the site.
Jesus, the Apostles and even regular Christians may be forced to publically use very offensive language because of what is at stake. For example if false teachers, are deceiving members of a congregation, very harsh language may be needed to rebuke them. If we just said, well they have their opinions, but we think we are right, others might think it is ok, to consider lies, in place of faith in Christ. Since the stakes are so high, leaders may need to let people know, chose them, or chose us, there is no in between. One is good, the other is scum, one if righteous, the other wicked. When it reaches climatic situations like this,** holy men will use the most offensive language, without ever needing to use words that are actually offensive in themselves.**