What do we call it when something is so obvious (about someone) that there is no point in stating it? Is there a phrase or an idiom?
It is very obvious that he is a drug addict.
An example of an idiom for "obvious" would be "as clear as day":
It's as clear as day that's he's a drug addict.
You can even use words like "clearly" at the beginning of the sentence to emphasise the phrase you're talking about:
Clearly, he's a drug addict.
It captures the same meaning as "It's very obvious that...", which is what you're looking for, it also adds a layer of emotion to the sentence as well.
In addition to Qwerp-Derp's answer, I found stand/stick out a mile which means:
to be very obvious or easy to see
I want to talk about something very obvious and recognizable about someone, so I can say:
His drug addiction sticks out a mile.
She sticks out a mile with her red hair.
One word is evident:
: clear to the vision or understanding
She spoke with evident anguish about the death of her son.
The problems have been evident for quite some time.
In your case:
It is evident that he is a drug addict.
Or a variation:
He is evidently a drug addict.
A longer expression is it goes without saying:
used to mean that something is obvious:
Of course, it goes without saying that you'll be paid for the extra hours you work.
In your case:
It goes without saying that he is a drug addict.
One idiom is “right in front of your nose.”
In your example, though, I think this phrase would be more likely to be used to emphasize the point rather than to state it outright. In other words, this wording seems rather clumsy, and I would avoid it:
It’s right in front of your nose that he’s a drug addict. → not recommended
However, the idiom can still be used effectively, if we add a bit of detail. For example:
It’s obvious that he’s a drug addict. The signs are right in front of your nose.
TFD defines the idiom as:
in front of (one's) nose
Immediately obvious or clearly apparent.
The solution was right in front of my nose, but I just couldn't grasp it.