If nerd packs and belt hangdowns instantly imply prole leanings, there are other signs almost as clear. When you’re wearing a shirt with a sweater or jacket over it but omitting a necktie, what do you do with the shirt collar? Keeping all of it inside both sweater and jacket is upper- or upper-middle-class, partly, I suppose, because the effect is “careless” rather than “neat.” On the other hand, displaying it spread out over the jacket collar, unless you’re a member of the Israeli Knesset or teach at the Hebrew University, is flagrantly middle-class or prole – and may be even then. All you really have to know about this practice is that when out riding or otherwise got up in sports costume … President [Reagan] favors it.
- Paul Fussell. Class: A Guide Through The American Status System, pps. 64-5. Emphasis added.

I love the Israeli dress code. I wish I were a guy just so I could do the open collar.
You can of course do the open collar, as long as you’re wearing something under it or over it.