Punctuation and the Apostrophe'

I can recall a funny (rather silly) incident from school days. What happened during the class is worth a mention.
You know these grammar classes have all these sentence correction exercises. The teacher had given us few sentences to correct with the subject and predicate kind of mix-up. Most of us were quite sure of what was to be done 'coz the discussion before attempting this was all about similar kind of 'common' errors. Somewhere near the end was this sentence. Please take a look:
This is Tommy's, my cousin's letter, congratulating me on winning the prize.
Now, should I give you time to correct this??

Well, the answer is : This is my cousin Tommy's letter, congratulating me on winning the prize.
All of a sudden RK had a doubt. See, most of us would care to interrupt only if we were getting the question wrong. Obviously RK had goofed it up. Here is what the discussion went like...

RK: Maam, this question has no errors.
Teacher: No. The answer I gave fits best.
RK: Why don't you consider this sentence: This is Tommy, my cousin. We need not rewrite it as : This is my cousin Tommy.
Teacher: When we have the apostrophe indicating possession we need to rewrite it such that there is no doubt.
RK: But...
Teacher: Okay, take a look at this sentence : This is my cousin Tommy's letter. All fine? Now, if you have to make a reference to something else which belongs to Tommy but you wish to indicate your relationship to Tommy as well then the use of two apostrophes is not correct. Thus, This is Tommy's, my cousin's letter, .....is not correctly framed. You will have to rewrite it sensibly.
RK: What if no sense can be drawn out of the sentence.
Teacher: What do you mean?

By this time all of us knew that the class was as good as over. None knew what RK had to gain out of this useless argument. Come what may, a teacher of English never modifies his/her answer 'coz its all there, written and maintained for ages. But what's the harm in having a little fun!!

RK: Consider this sentence: This is Tommy, my cousin's dog.
The class was in splits. Tommy was a poor little cousin writing letters to his brother/sister congratulating him on his success and now RK transforms him into a dog!
RK: And even this one: This is my cousin Tommy's dog. Isn't there a difference between the sentences?
Teacher: (Smiling) Well RK, we have been talking of inanimate objects here and you cannot mess it up like this. Do you intend to say this: This is Tommy's, my cousin's dog, congratulating me on winning the prize. Where on earth can this sentence make any sense to you?
RK: That's exactly the point I wanted to make. When we face sentences without any sense, we can get really confused.
Teacher: (Undisturbed) Teachers are not that bad. We do frame decent enough questions. Now shall we move on to the next question?
RK: But ma'am, what if we do face a question of this kind? (Now he was obviously having a little bit of fun) Shall we correct it like this : This is my cousin Tommy's dog. Or, shall we leave it as the original sentence : This is Tommy, my cousin's dog ? Tommy sounds more like a dog's name so I guess there is a little sense and this is what we should look for.
Teacher: (Definitely annoyed) RK, when there is nothing to correct in a sentence like that, we better not see them in any exam. We teachers are not here to have fun during exams but to test your application skills. You seem to be deviating from the point and the class' time is getting wasted. No more discussion please.

A few more questions and then the class ended.
This was one such incident. There have been weird discussions with nonsensical statements and arguments. Being in a all boys' school is real fun most times. Some teachers are bent on taking classes on sex education during their courses. Would like to share some of them later.