That's not what Paul said. Paul didn't say that ALL MEN become "vain in their imaginations." He says that those who hold "the truth in unrighteousness" (Ro 1:18) have become "vain in their own imaginations." (Ro 1:20).
Romans 1
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
19 Because that which may be known of God is manifest in them; for God hath shewed it unto them.
20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:
21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
22 Professing themselves to be wise, they became fools,
No, I think that Calvin correctly interprets this as ALL men!
Read vs 18 again: For the wrath of God is revealed from heaven against all ungodliness and unrighteousness...
The wrath of God is revealed from heaven against ~ALL~ ungodliness and unrighteousness.
More specifically -against the ungodliness and unrighteousness of men.
You will note, in the KJV, the comma after "men". (This is also supported in the Greek on-line interlinear at www.crosswalk.com.)
In other words, this passage is saying that God's wrath is revealed against the ungodliness and unrighteousness of men. And these men are also guilty of holding the truth in unrighteousness.
Another way to put it -do you know ANY man who does NOT have unrighteousness and ungodliness?
Isn't that confimred just a couple of chapters later?
Romans 3
9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin;
10 As it is written, There is none righteous, no, not one:
11 There is none that understandeth, there is none that seeketh after God.
12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
Jean