It's a part of the song Take Your Guess by Tom Rosenthal (lyrics: https://www.azlyrics.com/lyrics/tomrosenthal/takeyourguessalternativeversion.html) I don't understand this part of the lyrics (I'm not a native English speaker): "take your guess, spurious at best, can't you see it's all just chaos." Who is supposed to 'guess', and what to guess? And does it say "it's best if your guess is spurious/fake"? It doesn't make sense!
A caveat: song lyrics often have many possible interpretations, and this song especially is pretty ambiguously-worded; we don't get any completely unambiguous explanation of who is asking the question or what the guess is about.
(Though, from context, it seems that the guess in some way relates to the person the singer is referring to wanting to know the best way to live or the correct way to go about life: see lines such as I see a million ways and that's fine, which can be taken as meaning that there's no correct way to go about things.)
However, there is one part you're misunderstanding that I think will make the lyrics more clear: the phrase [X] at best when combined with an adjective or phrase that has negative connotations means that, even in the very best possible outcome or viewed from the very best possible light, the thing being discussed has that negative property. One example of this phrasing can be seen in this book excerpt:
Many parents also faced various persecutions from the party, suffering extreme stress at best and violence, imprisonment, or death at worst
So here, the book is saying that even under best circumstances the people suffered extreme stress. (And, under not-the-best circumstances, they suffered even worse.)
Taking this example and applying it to the lyric, we can see that the phrase take your guess, spurious at best means that, even in the very best outcome, the subject of the song's guess will be spurious (and in less-than-perfect situations, the guess could be even worse than spurious). The last part of the lyric, can't you see it's all just chaos is an explanation for the first part: because everything is chaos, any attempt at explanation will be useless and so the guesser's guess can only be invalid (or worse).
The song is about the unpredictability of life and how there's no universally right approach to it. You can spot this theme throughout the lyrics of the song. The whole song apart from the chorus follows this format:
"I didn't [do something or something didn't happen] how you said [I would do it or how something would happen], it [went the way it did] and that's fine"
It's saying that it's okay for things to turn out differently than expected or intended and to do things differently than what's considered normal or proper.
The lines "I look out the window somedays, I see a million ways and that's fine" and "I breathe in and then I breathe out, I've got a trillion doubts and that's fine" suggest uncertainty about the future, and/or the choices he has to face.
Therefore, by looking at the rest of the song, it becomes quite clear that the chorus is about the same thing. "Take your guess, spurious at best" means that if you try to predict what the future holds, you will realise that your guess is spurious, or in other words false and unreal when compared to what actually will happen. Don't you see it's all just chaos just means life is chaotic and full of unexpected twists and turns.