
Very Good.
I actually did my dissertation on this very subject. Thank you, I would never have thought of using it as an opener.
Come to think of it, when I was explaining it to a few girl friends they seemed to find find it very interesting even though I found it awfully trivial explaining it to them.
At the risk of sounding intelligent. Here is a bit of further info for conversation, hope it helps:
The theory is that it could be an accurate way of gauging androgen exposure early in foetus development, (this refers to the hormones that actually determine your sex i.e. testosterone/oestrogen). My actual thesis found that 2d:4d ratio can predict the depth of voice that a woman finds attractive, but its use has been further expanded into how successful people are in their jobs, how highly they rate their own physical attractiveness and a vast multitude of other factors that I won't bore you with.
On the most basic level what I deduced from carrying out my thesis is that women seem to be more attracted to men who demonstrate androgen exposure that they may be lacking in. I.e. a HB with relatively masculine androgen exposure may find more feminine males slightly more alluring.
Remember all embryos are initially female
Someone said earlier that homosexuals were more inclined to demonstrate feminine ratios, with a bit of speculation we can say that the reason they are homosexual is primarily down to the androgen exposure they received in the womb. Enough masculine androgen(testosterone) exposure to result in maleness but not enough to change the sexual cues that they find attractive.
So if you want to work the whole 2d4d ratio into a proper conversation, you could possibly neg them, by telling they should be into chicks. Or compliment them by saying they will go far in life, or "wow, your ratio is huge!! you must be super confident".
If you can think of any other ways to hit them with this concept let me know.