Look at this video : https://www.youtube.com/watch?v=_GVNnkhGAiE How do I put it into words?
For example : Girl waving her hair sexily?
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This is commonly known as a hair flip or flipping the/her hair. For example:
There is a very important, crucial-to-your-life topic I'd like to discuss today: hair flips and how to do them all sexy, Victoria's-Secret-style. (Beth Shapouri, "Let Alessandra Ambrosio Show You How to Do a Hair Flip Like a Sexy, Sexy Boss", Glamour, October 29, 2014)
These photos of Amal Clooney demanded a new BK Thread dedicated to Champion Hair Flipping. Only the very few know how to employ the hair flip with such aplomb. ("Championship Hair Flipping/Flinging", Bitter Kittens blog, March 2015. Note that while the title includes "flinging", virtually all examples from the extensive entries in the thread use the verb flip exclusively. Check out the link for many, many images of hair flipping.)
The mainstream dictionaries haven't quite caught up to this usage, but Urban Dictionary has at least two relevant entries:
what girls do 2 get attention from any cute guy looking at them, a form of flirting
hair flipping elaborate dark ritual used to attract male humans. Many techniques of hair flipping exist. consult a veteran hair flipper for advice.
Please note, however, that a hair flip is not necessarily meant to be provocative or flirtatious; it can also just be a way to get the hair out of the eyes, a nervous tic, etc. (When I do it, it's very often because I've got my hands full with a baby and a dirty diaper, and I'd like to keep both out of my hair—pretty much the antithesis of trying-to-be-sexy.)
As the second definition above suggests, there are a lot of variations on hair flipping; the one you linked to is a slow-mo(tion) hair flip (see Google video results for many examples).
This style of letting-down-the-hair flip was used extensively in the original Charlie's Angel's television show, and the 21st century movie version capitalized on this with the slow-mo version, as in Lucy Liu's version of the iconic clip of Jaclyn Smith removing a helmet in the TV show's credits.
As I recall the cast talked about "hair flipping" in interviews at the time, and the phrase even made it into the script. From Wikiquote:
(Natalie is flirting with Pete, the bartender. The Angels are communicating via Walkie Talkie)
Alex: (quietly) Flip your hair. Natalie: What? Alex: (quietly and impatiently) Flip. Your. Goddamn. Hair.
(You can see a very poor quality video of the scene here. Probably NSFW.)