Macdougal: You know, laddie, no Scotsman puts sugar in his porridge.
You: Is that so? I seem to recall my cousin Angus puts sugar in his porridge.
Macdougal: Ah... but no true Scotsman puts sugar in his porridge.
A strange but very often used example of trying to persuade without any particular argument to back up your claim - simply redefine your terms so that you win! In the above, Scotsman has been redefined to mean "person of Scottish descent who conforms to particular cultural expectations, including the eating of unsweetened porridge". The argument then becomes "No person of Scottish descent who conforms to particular cultural expectations, including the eating of unsweetened porridge puts sugar in his porridge" - true, but not particularly profound.
For the original source of the argument (using an example that has nothing to do with porridge!), see en.wikipedia.org 
This kind of argument is sometimes used by OO purists - the article www.javaworld.com redefines the term "Object Oriented" to refer not to virtual methods and polymorphism, but to the direction in which data flows through the program (Tell Dont Ask) - an important concern, but nothing to do with OO. Ok, this is just foolish. Arguably the main theme in Simula/Smalltalk is "sending messages to objects". Tell Dont Ask is the very basis of OO. But it's not the same as simply confusing two different things, it's a matter of redefining words to be other than their obvious meanings.
This can't really be categorized with the rest of the Fallacious Arguments because it isn't logically wrong to reason like this, per se. "No Scotsman who doesn't put sugar in his porridge puts sugar in his porridge" is a true statement. But using a No True Scotsman argument is nevertheless dishonest and sneaky and cowardly, and I wouldn't recommend it.
Actually this does belong with the rest of the Fallacious Arguments. Depending on how it's worded, it's a tautology, an example of Circular Reasoning (as restated above), or Failure To Elucidate.
Concur. Failure To Elucidate seems to be the closest match here.
Part of the problem is the just the nature of the industry in which terms such as OOP, OODBMS, architect, business analyst, etc. have no uniform, clear, and agreed-upon meaning. People develop their own personal definition and "rules" and then assume or hope that others will agree.
A variation is, "If you did X right, then my definition of X is the correct one." This then takes us into verifying "right", which is probably a much harder problem than mere defining.
Friedrich Nietzsche described something akin to No True Scotsman in his On Truth and Lies in a Nonmoral Sense:
"When someone hides something behind a bush and looks for it again in the same place and finds it there as well, there is not much to praise in such seeking and finding. Yet this is how matters stand regarding seeking and finding "truth" within the realm of reason. If I make up the definition of a mammal, and then, after inspecting a camel, declare "look, a mammal!' I have indeed brought a truth to light in this way, but it is a truth of limited value. That is to say, it is a thoroughly anthropomorphic truth which contains not a single point which would be "true in itself" or really and universally valid apart from man."
From my point of view it's true, since as a Scotsman, the idea of waking up in the morning to a bowl of oats with lukewarm water in them is my idea of hell. Crack open the pop tarts!
(You forgot to add, "laddie")
If It Aint Scottish Its Crap.--Stuart Mackenzie
ahhh you got to love the scots, they are a good bunch of laddies and lassies and have a historical wealth of knowledge behind them. Jock
Ach, laddie, Scotsmen wear nothing under their kilts! That's right, for twelve hundred years our testicles have been hiding. God bless global warming, lad!
"But what about Scotswomen? Surely it does ya nae good to have your mollusc trembling all the time!" And therein lies another problem that finds mediation in a return to the ancient ways : this Angle-ish has no unsexed personal pronoun! Looks like we'd best start with the Gaelic in schools again.
Jost doon't be callin' it a "skirt". The last man whu done that - he got kilt!
I've always said that No True Scotsman was unsound because it is attempting to make unsupported distinctions. They try to convince you to make the distinctions found in their definitions without you ultimately knowing why they are being made at all or how they are supported. It is because it is what I said it is! Sure, whatever you say...
See: Laynes Law
See original on c2.com