American English colloquial slang?

For some reason I prefer American accent, but British way of speaking sounds "more correct", if I can say it that way.

Well, it probably just sounds "more correct" simply because you were likely taught specifically English English, and taught, of course, that the various expressions and usage patterns and like in it are what's "correct", of course. That's just like how the overall usage patterns that I'm used to here in Wisconsin sound "correct" (and likewise various English English patterns sound rather weird to me, at times, honestly), simply because I'm used to hearing them (and in the case of the "high" register, reading them) primarily, and having learned them natively as what's "correct", simply due to the dialect here being effectively my native dialect. That is, of course, analogous to your having likely been taught English English norms with respect to usage, as a whole.

There are many possible reasons, but the rhoticism and very different pronunciation of almost every word stand out as the main factors. Spelling is another, but probably not one which annoys Europeans.

Well, one major part of that is that, say, Central Northern American English has a completely different phonemic system to start with, with respect to vowels, than English English dialects in general, with many vowels in many places merging together, such as in the "Mary"-"marry"-"merry" merger, and some vowel phonemes completely merging with others altogether, like in the "father"-"bother" merger. In addition, English English historically has severely reduced or removed many unstressed vowels which have been preserved in many or most American English dialects, while at the same time, American English has historically lost /j/ onglides in many places, and in a modern context has a strong tendency towards reducing both intervocalic and word-final consonant clusters, and also in a modern context has a tendency to reduce vowels by removing them altogether, and simply syllabifying the following consonant, when syllabifying said consonant is possible, in many cases.

It wasn't always so. For example the rhoticism was much less evident in NA speech just a few decades ago: in old television shows from the early fifties the speech of the male characters is non-rhotic, and that of the women shows just a hint of the rolled R which now ranks with the disappearance of the short A and the short O as the major differences between NA English and other Englishes.

Well, part of that may not be solely due to direct change alone in various North American English dialects, but rather due to shifts within dialect patterns in North America, where features from some dialects have been become more common in other dialects, for example, the spread of rhoticism within North America, where many formerly non-rhotic dialects picked up rhoticness from rhotic dialects such as Northern Central American English, what was formerly called Northern Inland American English, but I'm using the term Northern Central here, as the term Northern Inland is used by some today to refer to specifically dialects that have had the Northern Cities Shift, while Northern Central is used to refer to such dialects in the former Northern Inland group which never had said shift.

Rhoticism or rhoticness is such an important and increasing difference between the major Englishes. In some respects it's easier to speak rhotically, inasmuch as the intrusive [r] is much easier for a lazy speaker to insert between vowels than a carefully-controlled brief and unvoiced glottal stop, so that even educated native English speakers in Britain and Commonwealth countries use it often, but invariably continue to use ultimate [r] only as a guide to the pronunciation of the ultimate vowel, which makes the final syllable easier (and shorter) to pronounce.

I can't decide between rhoticism or the two versions of the short A used in NA ("fast" and "can't") used instead of a really short A (northern England) or long A (southern England and Commonwealth) as the most annoying.

At least here in Wisconsin, the only difference at all between the vowels in "fast" (/f{st/ --> [f{s] or [f{st]) and "can't" (/k{nt/ --> [k_h{~?]) are that the second vowel is realized as nasalized, whereas the first isn't, and that isn't even a phonemic difference (even though it could very well become such in the not-so-distant future). Mind you though that the nasalization here is important for understanding the word, even though it is not phonemic, for if it is omitted, at least here it will probably be heard as "cat" (/k{t/ --> [k_h{?]) rather than "can't".

Interesting, Travis. Please forgive my failure to display pronunciations in correct symbols, but my experience, and none of it may have been in listening to people from Wisconsin, has been that the two sounds are quite different. Both short, but easily distinguishable from each other.

To me, the vowel in "can't" rhymes with "dance" (as spoken by Americans I have heard in person and on TV, movies etc., while to my ear, they pronounce "fast" to rhyme with "last", "past".

The interest being in the fact that Yorkshiremen, for example, pride themselves on their extremely short As, and that they produce exactly the same vowel for both those words, yet NAs, who don't use the long A (ah) used in RP (or SB) and in other former British colonies, for one or both, have somehow stretched the short A into two distinct nasalised phonemes.

Oh, I should have marked that in my phonetic transcription of "can't", but the thing is that the vowel in "can't" is also long, whereas that in "fast" is short. This is not a phonemic quality of the vowel itself, but rather one that is simply a consequence of if the coda for any syllable start with a voiced consonant, the vowel is realized as long, whereas normally it is short. Hence, as /n/ is voiced, in both "can't" and "dance", the vowel in those is long, provided that one doesn't elide the /n/ in "can't", which I myself do; I myself consequently normally pronounce the vowel in "can't" as short rather than long, but pronounce the vowel in "dance" as long. As for "fast", "last", and "past", as /s/ is unvoiced, the vowels in those are all short. The thing though is that as vowel length is not phonemic, but is purely determined by the syllable-level environment of any gien vowel, the vowels in "dance" and in "fast" are both "heard" as the same vowel by most North American English speakers, even though they really are not the same vowel at a phonetic level, as the former is long and nasalized, and the latter is short and nonnasalized.

Ack, I should have said that the vowel in "can't" here is also long *provided* one actually pronounces the /n/, that is, if one does not elide it and simply leave the vowel nasalized alone, as I do (and hence why I pronounce it with a short vowel).

"the rhoticism and very different pronunciation of almost every word stand out as the main factors. "

I like the New York accent for that reason - It's less rothic...

I consider Bush's accent the most annoying...

I don't think I've ever heard the /n/ in "can't" elided; would you elide it also in "cant" (no apostrophe", or in such words as "hand", sand" etc?

I would elide it in "cant" (no apostrophe) myself, but not in "hand" or "sand", where when not speaking slowly it's likely to simply merge with the following /d/ instead, which when in a final position is generally normally preserved, unlike /t/, which becomes [?] in that position, resulting in the word ending in an [n] which is *not* elided, for it is the simple reason that the /d/ after the /n/ becomes part of the [n] by becoming nasal, but does not lose its stopness in the process. This [n] may very well be [n_}], and to be more stop-like than a normal [n] that is not in stressed-syllable-initial position, which is likely to be more vowel-like in quality, when it isn't simply elided altogether.