I seem to be a little late in coming across this trend (it seems to have started around the 9th of September) and usually I disapprove of anything which dictates how a woman's body should look. But a thighbrow (please, someone, come up with a better word) is something that everyone has, regardless of body shape or gender.
Why do I find it so sexy? Firstly, it's because it is so very aesthetically satisfying. A thin, dark crevasse in what is for most a perfectly smooth part of the body. Secondly, it is much like the obliques (which I have previously celebrated here). On both sides the lines start at the top of the hip and end at the groin, a suggestion of what lies beyond the underwear.
Trends such as the thighbrow are often mostly negative in that they objectify women (not in the fun way) and make people feel pressured or unhappy with their bodies. As this particular trend can include everyone I'd like to turn it around and make it a positive thing - a celebration of the beauty of the human body.