先生「これだけは覚えておけ、Do you surfing with me? だ直訳すると俺と一緒にサーフィンしないか?と成るだろう?しかし真意は違うアメリカにはウォーターベッドの文化がある。そこでSOXする時にまるでサーフボードに跨る様に成る。その騎乗位形から真の意味訳は『俺とS〇Xしないか?』と言う意味に成るんだよ。これだけは覚えておけ。」
I can’t emphasize this enough, but to each their own, I guess. I think learning grammar is not unnecessary for adults who are trying to learn English as a second language, which is the fact that brain science has proven so far, but he hasn’t mentioned it. It sounds kinda risky to say grammar is unnecessary, dude..
I'm against your opinion that English grammar is not necessary to master English. With regard to acquiring a second language, there is so-called Critical Period Hypothesis. According to this hypothesis, only children under a certain age learn to speak a second language without its grammar, that is to say, by the method you are referring to.