The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
OP has said it's not that; it's about the mundane concept of flexibility.
If it's something like "wow, imagine how good gymnasts are in bed" then it could be Inherently Attractive Profession.
Inherently Attractive Profession could work, although I think there may be enough there to possibly qualify as a separate trope. I'll see if I can track down enough examples to take to Launch Pad. Thanks!
A man is describing an attractive woman, and one of the most attractive things about her is how flexible she is. Seems to be used as a way to imply having wild sex without actually giving any details. Not Contortionist or Rubber Man (this is specifically about the attractiveness of flexibility, not flexibility itself), not Power Perversion Potential because it's not about superpowers.
Example, from the show I'm working on a page for: "My little acrobat girl, the things she can do, she's made of rubber, she's incredible." But I'm pretty sure I've seen this several times in other places as well.