That's hilariously vague, no one's going to bother with that description. You didn't even mention her skin color, what she was wearing, whether she was a giant bodybuilder or a small figure model, what type of leg flex she was doing (calves, quads, hamstrings), etc.
[Locking this thread, as it's immensely useless and OP doesn't seem inclined to add any more info]
I saw a video on here once but I can't find it now. It was a video of a girl with short black or brown hair and glasses flexing her legs on a couch. I believe the couch was red or dark colored.