I hope this is the right place for this (first post started):
I have been challenged with explaining a few oxymorons & seemingly contradictory phrases.Any help on these appreciated, with sound reasoning if possible:

Can fat people go skinny dipping?
Why are buidings not called builts when they are finished?
What does the same difference mean?
If you're on an American airline, and you land in Canada and stay on the plane, is the drinking age still 21 or does it change to 19?

I've got many more but help on these would be a start

Well, the first one... it's kindof a thoughtless question, but here's the answer: Skinny doesn't only mean thin, of course. I believe it has been used as a slang for naked (and perhaps in that way also related to the use as in "get the skinny on" which is to get the bare facts) and in that usage, of course, anyone can go skinny dipping. Skinny, as in "in the skin".

The second question: Why aren't paintings called painteds when they're finished? Why aren't weavings called weaveds when they are finished? The simple answer is, the word building is not only a verb. Why that is is something we probably will never know. It's part of the way the language is structured, and you'd have to ask those dudes a few centuries ago why they did it that way.

With the fourth question: I believe that whereever you are, that's the drinking age. That's why a 20 year old can drink on an American cruise ship in international waters. The plane is on Canadian soil, so the local laws apply, but that doesn't mean they'll actually serve you alcohol... I mean, the question is moot because why are you staying on the plane, and do airlines serve customers liquor in between flight boardings?

We'll confuse you further, as in my part of Canada, the drinking age is in fact 18!

I don't think this question really makes too much sense when applied to air travel, as the planes don't serve liquor when on the ground. However, it is very applicable to train travel. On the train, the liquor laws of the province through which you are travelling (in Canada) apply. In theory, this means that if you go from a province where the legal age is 18 to one where it is 19, you should lose your drink at the border. In fact, this does not happen. You get to finish your drink, but if the server knows that you are only 18, you won't get another. I have found that in general, young people who do not draw attention to themselves can continue to drink quietly even after crossing a provincial border.

Gosh how are the servers supposed to keep track of
a) which state they are in
b) what the drinking age in that state is
c) the age of each passenger

Sounds too complicated.

Found this explanation @ randomhouse. Thought it explained it rather well.

Same difference means 'same thing; no difference'. No one can say for sure how the expression arose, but very likely it was through a blending of those two phrases. These formulaic expressions are fads; they come and go. People today are more likely to say, "Whatever."

Apologies in advance, but besides acquired tortologies, where people refer to acronyms and then name one of the elements which is already included in it such as PIN number, where N is already for number, or LDV vans where the V is van, one which has always got me is the euphemism for incontinence 'Gone to the toilet in your pants'. Now you can either go to the toilet or in your pants, but what it says is not what it means.

I'll get me coat...

It might not be what it means but everyone understands, although it isn't what I would say. I might say "David soiled his pants" or "David wet himself" or even "David has had an accident".

Sue, are you suggesting I'm incontinent?!

Actually, the last time that happened...

As if David.

Thanks for the attempts to assist me in my quest which consisted of me replying to approximately 100 similarly daft questions. I managed to find answers to all of them in the end,some far sillier than others (I did use parts of the answers on here for a couple).

Regarding the toilet problem I would suggest 2 possible routes:

1.Maybe the toilet in the pants refers to some lost sanitary world akin to Narnia which can only be accessed via a gateway contained within the pants(possibly the zip).
2.Given that the word toilet originated from cloth, maybe the expression is smarter than it intended, and refers to a portaloo of sorts which is the material contained within the pants.

I'd go with that maggotbrain, you have shown you're just the kind of person that belongs on Funtrivia And managing to turn sloppy English into a semi-official and technically possible explanation would also make you a very good politician