I remember that Clint and Natasha were enacting dance dares. I think, once, Nat actually danced behind Pepper when she was in the office or something. The reason Nat and Clint did the dance dares was because they noticed that Tony was sad and they hadn't seen him smile in ages.
I remember really enjoying this fic coz it was actually quite hilarious.
Do you guys know which fic it is?
Edit: Found. Link in comments.