In Japanese, being offensive is also through grammar (conjugating certain words in less polite ways than normal).
English is just as much on a continuum.
But these taboo words would only be used to specifically refer to their actual meaning, they aren't used to express generally strong emotion the way that swear words are in English. 2) A word can be translated many ways depending on context. Tangentially, any time you hear someone say [their country] is special because [reason], there's a high chance they are wrong. Even in fiction with modern settings. Fart in Japanese. It's hard to relate to English, but think about how the "nyah see" mob bosses talk, or the "well I do declare" southern belles talk and how you immediately know what kind of archetype you're dealing with... except it's much more common and not just in shows aimed at little children. A teacher once chuckled at me for using joseigo. Maybe that's just the rules of the broadcaster, but it's still a distinction between rude and too rude. Modern slang can be considered crude and vulgar to the elderly. Maybe not so fucking much. Instead they will use different grammar/vocabulary in expressing themselves, though the words used to express very strong emotions usually aren't in and of themselves taboo. Japanese has many many ways to show these feelings.
There has been... a certain poster... who is very enthusiastic this month about teaching this sub the secret swear words your teachers conspire to hide from you. For an example, for Japanese speakers (in my personal and limited research) the word ass and the word fuck have the same 'weight' when it comes to taboo-ness.
Most of the Japanese swearing don't contain actual swearing words like f-words and mostly depends on your tone, intonation and the circumstances the phrase used.
This post I'm sure also contains some mistakes and misconceptions, and I look forward to learning in the comments. Another thing I'll add is that it's not normal in Japanese to use sexual metaphor to insult people most of the time. You may feel that it is worth learning some insulting words in Japanese, but the reality is that most people don't need to learn them.
What he said would be totally okay among friends, maybe even feel friendly, but in class to the teacher was rude. I'd be interested to know why this is, since it sounds like the equivalent of people using half century old hippy slang and saying "Far out, man! I hope to set some things straight, and I hope native speakers and advanced speakers will also join in the conversation to correct me where I'm wrong.
Here is my response from a very similar question a year ago, reprinted (and slightly reformatted since it appears you can read kana) for your reading ease and pleasure: First of all, I think you need to have some contextual understanding of what swearing is - in English essentially it's using words that are considered taboo, usually to express a very strong emotion (disgust, pain, anger, etc.).
Part of my thesis is how Americans perceive English swear words and how Japanese perceive swear words. I've noticed this with lot's of foreign speakers, not just Asian languages. Or to be more generous to the speaker, they may be interpreting facts in a way that favors their feelings of uniqueness but is at odds with an impartial analysis. The biggest difference in my opinion is that the supposedly equivalent "curse words" in Japanese aren't inherently 'cool' because they aren't taboo in the first place. or "shit!". This is actually pretty analogous to English polite language about the same thing: most people I know are more comfortable referring to "Jewish people" rather than "Jews", "Japanese people" rather than "The Japanese", etc. 3) Japanese doesn't really have "swear words" in the sense that English does. Yet none of the Japanese words used in those phrases, くそ, バカ, がき, or ボケ are particularly taboo. I'd rather move on to a discussion of why exaggerated 役割語 (relative to other languages) is used at this point. Well done! I didn't mind because it closely preserves the feeling of how I talk in my native language.
There are other ways to sound cool by using inappropriate or socially-unacceptable language, and curse words usually are too simplistic to sound smart. 2) A word can be translated many ways depending on context. Looks like you're using new Reddit on an old browser.