The most anally perfect form would be "I make a house with 14 LEGO pieces.". But "I make a house with 14 LEGOs" is just as valid as "You're about to do what? You can't do that!" against "You are about to do what? You can not do that!".
Not true, It would be like, as previously stated, saying lets make a castle out of some sands.
there are different types of nouns, and as it happens, LEGO is not a countable noun. There isn't a degree of incorrectness about it, its quite alright to shorten cannot to can't, but it's against the rules of grammar to use LEGO as a countable noun, i.e. LEGOs. Also, because it is a brand name, you do not get free reign with how you use it. If anything, there are more stringent controls over how it should be used, those as supplied by English standard grammar and those as supplied by the company which owns the brand name. It's not a matter of whether its silly saying its wrong or not, it just is wrong, that's the point.
Oh my god, we can't say it? SOMEBODY TELL ALL THE TEN YEAR OLDS!
The fact is, language is not permanent. We have very little control over how language actually forms and changes. The rules need to adjust themselves to the usage, not vice versa. People have been calling handkerchiefs 'kleenexes' for decades. How many people do you hear asking for 'handkerchiefs' nowadays as opposed to people asking for kleenexes?
Aside from that, your assertation that 'you do not get free reign with how you use it' is utter and complete bullshit. Sure, if I try to release a product named 'LEGO' I'll run into trouble because the name is trademarked. That doesn't stop me, legally or otherwise, from using the word LEGO in any way that I damn well please as long as I don't claim to 'own' the word. LEGO LEGO LEGO LEGO LEGO. LEGOS. LEGOS LEGOS.
Better call the police, apparently I've just violated the law.
Personally, I don't care how you use a word, or don't use it. I was saying that technically, it was an incorrect usage. You say LEGOs if it makes you feel happy, but according to grammar, which does indeed change but not upon whim, it's merely incorrect. I'm saying there is no question about that. As to your example, I've never said Kleenex instead of handkerchief or tissue, but maybe that's because I'm English and don't see Kleenex around as much as I might.
As I say, for me this isn't a question about how people use the word, I couldn't care less quite honestly, it's just people saying they can say it how they like and it will be correct. they're right partially, say it how you like. That, however, does not make you correct.
It are possible me for talk grammar without. However, it generally helps if I stick to using grammar as it should be used, no matter how flexible you perceive it to be. Oh, and I'm not ten