Could you please tell me the meaning of "I took one look at him" in this excerpt from The Great Gatsby? Is this an idiom which is used when one thinks he can make a quick "snap" judgement about someone, that the guy he is looking at / talking about had a fairly distinctive style or appearance which the person looking at can evaluate quickly?
“Mr. Carraway, this is my friend Mr. Wolfsheim.”
A small flat-nosed Jew raised his large head and regarded me with two fine growths of hair which luxuriated in either nostril. After a moment I discovered his tiny eyes in the half-darkness.
“—So I took one look at him,” said Mr. Wolfsheim, shaking my hand earnestly, “ —and what do you think I did?”
You are quite right that "i took one look at him" is an idiomatic expression and means approximately what you infer. It used to be far more commonly used in the 1920s and 1930s, but for some reason it has faded out of popular American usage, like so many other popular expressions. The formula, "I took one look at him," or "I took one look at her," usually implies a feeling, a first impression of a person. This feeling or impression can be positive or negative. It can be very strong. It used to be popularly believed that one's first impression of another person is the best guide to judging that person's character.
Meyer Wolfsheim is a shrewd judge of people, and his apparent reliance on first impressions is not a bad one. Schopenhauer, the highly influential German philosopher with whose writings Wolfsheim may have been acquainted if only by hearsay, wrote an essay titled "On Physiognomy" in which he states:
Accordingly, it is, strictly speaking, only at the first glance that we have the purely objective impression of a face and thus the possibility of deciphering it. . . . We should, therefore, pay careful attention to such impression and should make a note of it and even write it down in the case of those who are personally of importance to us, that is, if we can trust our own sense of physiognomy.
Nick Carraway is judging Meyer Wolfsheim at the same time that Wolfsheim is expressing his earlier judgment of Gatsby and probably simultaneously watching and judging Nick Carraway.
You might be interested in knowing that the expression "I took one look . . ." is included in a still popular song composed by the famous team of Rodgers and Hart for the 1927 musical titled A Connecticut Yankee. The song is what musicians call a "standard." It has been recorded by such celebrities as Frank Sinatra and Ella Fitzgerald.
The song's title is "My Heart Stood Still," and the pertinent lyrics are:
I took one look at you, that's all I meant to do
And then my heart stood still,