"The Very Best Pronunciation" or "How I Learned to Stop Worrying and Love [kʰeɻioʊki]"

When I go to a restaurant of foreign cuisine, I like to show off my knowledge of the appropriate foreign language. It's one of my character flaws. Usually this only extends to pronunciation. In a Japanese restaurant I order [soba] and [tem:pɯɾa], not [soʊbə] and [tʰɛmpu:ɻə]. In a Chinese restaurant I ask for [szˌʈʂwantoʊfu], not [sɛ:ʃwantʰoʊfʊu]. That's why when Yumeko ordered a [kesadija] (instead of a [kʰeɪsəɾijə]) at Qdoba, I assumed she was doing the same. But something seemed different in this case. So I asked why she said it like that. I asked if she would have ordered a [bur:ito] instead of a [bɻˌiɾoʊ].

Yumeko proceeded to get very offended.

This has, in the intervening time, raised several questions in my mind.

1. Why did her usage seem strange to me; am I just a big hypocrite?
2. Why did she get so offended?
3. How should speakers of Target deal with loadwords from Source? When speaking to speakers of S?
4. What should the speakers of S do?
5. On whom does the responsibility fall?

Before I attempt to explain or answer these questions, allow me to provide some background.

I believe that for any utterance in any language S, there is a certain best, or perhaps a certain few best, pronunciations of that utterance which firstly obey the phonology of T, but which are optimally close to the original pronunciation (meaning the borrowing is a phonetically faithful, not a phonolgically faithful). One of the problems is that what sounds closer to the speaker of S is quite different from what sounds closer to the speaker of T. The Korean surname [kim] sure as hell sounds like [kʰɪm] to me, but I think most Koreans would agree that, if forced to choose, [gi:m] or [gɪm] is way closer. The orthographic choices are no help either, because they are subject to great variation, and tend to be phonological transcriptions into an ill-equiped alphabet. But not always. More on all this in a bit. Now to the questions.

1. I think that when I use my native pronunciations, I do it for two reasons. I foolishly think I am being helpful, because the person taking my order probably speaks Japanese or Chinese etc., and because I associate these food items with the language, because I was probably introduced to them in the course of my study. The more I think about it, the more I realize it must be really annoying. But wait, hear me out. Anyway, the reason I thought Yumeko's use was odd was because the person taking the order did not speak Spanish, so it seemed somehow pointless, or even arrogent (as if it's not when I do the same).
2. Firstly, the reason my assumption was wrong. Yumeko informed me that, unlike me who has eaten quesadillas all my life, she was only introduced to them during College, which was after she had started studying Spanish. She just didn't know that it was common in English, and was not accustomed to pronouncing Spanish words in an American way. By pointing it out I was not only calling her arrogant (go figure), but also rubbing in her face the fact that there were just a few itsy-bitsy details of English that she had yet to discover, even after more than a decade in America.
3. I realize now that I'm probably not being very helpful to pronounce 'soba' and 'tempura' in a Japanese way, probably not to anyone. I'd still like to show off, though. And less savvy English speakers? It's probably not resonable to expect anything outside of the T's phonology, so can we expect the closest pronunciation, as mentioned above? It requires the council of a native speaker of S, which most speakers of T will not have access to, and a level of linguistic awareness that most people are not accustomed to. But I think we can all agree that 'burrito' and 'quesadilla' have found their place in English and should be used like any other English word.
4. Or not. I remember a woman came to speak at my highschool about Latino rights. She spoke English fluently and with no accent. Except on Spanish words. Then she would use a full blown Spanish accent. Even Spanish words that were already well known to English speakers, notably words such as 'Latino' and 'Mexico'. It seemed that she very much preferred the Spanish pronunciations, and would be delighted if I used them. But she was trying to make a point about ethnic identity. So what should Yumeko do, when she is discussing Japanese things with an English speaker? For words used in English often, the answer is easy. Pronounce 'sushi', 'samurai', and 'sake', like Americans do. And words that are never used in English? Probably it's best for the speaker of S to make that critical judgement and choose the best approximation in T's phonology. But then again I'm assuming the speaker of S is a native speaker of T. There's just no winning here. The most interesting cases are those where Yumeko uses a Japanese word which is well established in English, but which she has never heard used in English. A word like 'doujou' or even 'anime'. And Yumeko is always struggling with the pronunciation of her name (how to say it to others, whether to correct people), which I imagine is common. Anyway, the likewise question, which is much more important, is how should I pronounce English words when I speak Japanese? Just throw them in with American pronunciation (and not be understood), or katakana-ize them?

Oh dear, I have resolved nothing, and thoroughly confused myself. I realize that the question of best borrowing pronunciation is not applicable to most of the above examples, so I will provide a few more, namely 'karate' and 'karaoke'. In American English we really butcher these, despite the fact that there exist much better approximations within English phonology. Something like [kʰaɻatʰeɪ] or even [kʰaɾatʰeɪ] if you can handle it (after all the flap does exist in English), and likewise [kʰaɻaoʊkʰeɪ] or [kʰaɾaoʊkʰeɪ]. In the end, is the speaker of T responsible for providing a good pronunciation, or is the speaker of S responsible for knowing what the word is like in T?

I know I'm coming from a narrow point of view, so I'd love to hear from others who have more and different languages that they interact with on a regular basis.

p.s. Anyone know how to get those syllabic marks under the letter?