上下左右 (じょうげさゆう). Means "top, bottom, left, and right". It isn't used very often, but it's useful for talking about web design, which is how I first encountered it.

拘り (こだわり) when used for food. It's easier to translate it as a verb (拘る), which means to be particular about something. 玉子に拘っている can very simply be translated as "We're particular about eggs", but 拘りの玉子サンド is much more difficult to translate. In this usage, it means that lots of care, thought, time, and/or work has been put into getting it right. There are a few translations you could use, but I don't think any one of them had quite the same nuance. Jim Breen dictionaries translate them as "speciality", but I don't think it captures the original meaning at all. You could translate it as "artisanal" or "finest", but that gives it more of a high-end or luxury sounding nuance. "Meticulously crafted" is also close, but that sounds like something very complex or elaborate, whereas the original can be used for simple things.

Both characters have the same meaning in this case, so it probably doesn't matter. I think 花金 is more common.

I was once wondering around a neighborhood in Tokyo and passed by a group of friends who were saying goodbye to each other. I heard one of them say "お疲れヤマ". I stopped, wondering if it was some strange kind of slang or regional variation, but she then started laughing and said "お疲れマウンテン".

代々墓 (だいだいばか): An ancestral grave

One of my Japanese teachers pointed out that it's often used in sentences like OO家族代々墓, which makes it sound like " the OO family are massive idiots.

I also thought 五十五 sounded funny when I first learned it, because I thought it was supposed to be pronounced like "go Jew go".

It probably doesn't make any sense noq considering how quickly internet language changes, but I learned the word for ambulance (救急車　きゅうきゅうしゃ) around 15 years ago, and at the time QQ meant crying, and was used to call people emotional crybabies. It reminded of the term "wahmbulance" which people would use when someone is being whiny.

手紙 is the direct object. 家 is the place it was sent to, so I suppose that counts as an indirect object. Sentence order for Japanese is very flexible (although the verb must always come last), so I wouldn't worry too much about memorizing any particular order beyond Subject-Object-Verb.

Edit: I took a look at the source you gave, and I think you should probably disregard this sentence pattern. It's clear from the purpose of the lesson that they were purposefully trying to shoehorn から, へ, and に into single sentence. I don't think it sounds particularly natural.

When I had sex ed in the late 90's, I was shown videos with real (but obviously non-sexualized) nudity. I don't remember there being any controversy about that at all, and I went to a Christian school (Anglican).

I personally had one or two issues with the video you used. I'm not sure they were being literal when they said は means "as for". は doesn't have any meaning, it has a function. Translating it this way can help people understand how は works within the sentence, but I've also seen it confuse people too. I once saw a post from someone who said 私は難しい incorrectly thinking it meant "It's difficult for me."

Some of the things you mentioned also weren't accurate.

a) Generally speaking, cats are liked [猫が好きだ] b) As for me, cats are liked (-> I like cats) [私は猫が好きだ]

Sentence B is correct. Sentence A however is just sentence B with the subject/topic omitted. You'll have to infer the it from the context, but it will be "I" in most cases. I don't think there will be any context in which it will be understood as cats being generally liked by everyone.

a) Generally speaking, as for cats, everything about cats is liked. [猫は好きだ] c) As for me, as for cats, everything about cats is liked. (-> I like cats) [私は猫は好きだ]

There are a few issues here that are a little misleading. は好き can be used like this, but in my experience of looking at sentence from native Japanese speakers, it's mostly only used in the following three ways:

1. Comparisons, for example 私は猫は好きですが、犬は好きではありません (I like cats, but I don't like dogs.)
2. Together with a conjunction like ですが、ですけど、でも, for example 私は猫は好きですが、飼ったことはありません (I do like cats, but I've never had one.)
3. Together with になる, for example 私は猫は好きになれませんでした (I wasn't able to become a cat lover.)

Number 2 and 3 can be replaced with が, but は is preferred for number 1.

私は猫が好き also doesn't quite mean you like everything about cats. It's the same as saying you like cats in English, you're making a general statement without specificially identifying what you like about them. I like everything about cats is closer to 猫の事が好きです or 猫の全てが好きです.

I'm no expert on this, but in addition to the other factors people mentioned, I would say that people in Japan seem to pay a lot more attention to high school sports. The Koshien Stadium and the high school baseball tournaments name after it are very famous. I'm not even interested in sports, but I know about them and often notice friends talking about them online. I know absolutely nothing about the college baseball tournaments or where they're held.

As I mentioned in my other comment, I assumed they were the same, but several sites said they were different things. "American coffee" is a weak brewed coffee, and Caffe Americano (アメリカノ) is a diluted espresso, which is actually stronger than most brewed coffees, at least in terms of caffeine content. Japan has アメリカノ too, and in my experience it's much more common.

I thought maybe it was supposed to say Americano, but it's not the same. There's an explanation here. It's made from light roasted beans, and they say it most likely got it's name from Americans in post-war Japan brewing coffee with lots of water or diluting it further before drinking.

I'm not American, but the name sounds a little judgemental to me.

I'm not a native speaker, but I've studied Japanese for more than a decade. There are no singular, non-gendered third person pronouns, so there is no equivalent of a singular they. Although there is an equivalent of a plural they, it's not completely gender neutral. The equivalent of him is kare, and the equivalent of her is kanojo. You can make them plural by ending "ra" on to the end of them. Kanojora is used only for groups of women/girls, and karera can be used for a group of men/boys, or a mixed-gender group. That makes the root meaning of karera male coded even if it's used in a gender neutral manner, so non-binary people might prefer not to use that.

This shouldn't however be a major issue for Japanese speakers, as first person pronouns are the only ones that are in frequent use. Unlike English, where you use pronouns to avoid repitition, you can completely omit them in Japanese, so instead of asking "Has Asami done her homework?" in English, you would ask "Has Asami done homework?" It's also preferable to use names instead of 2nd/3rd person pronouns. Instead of asking "How about you?", you'd ask "How about (person's name)?" It's probably much easier for a non-binary person to ask that no pronouns be used for them

Why were they so sure the penguins weren't just roomates?