Remus had loads of little quirks that no one knew about but he was secretly really proud about; He knew impeccable sign language, he could read in like, 5 different languages, he was actually a really good singer, the list goes on.
The one time he ever explicitly used one of these many talents was when Sirius lost his voice, Remus convinced him that he was learning how to sign "I lost my voice because I'm awesome" when really he was learning to sign "I have a huge crush on Remus". This was back in second year when Remus was coming to terms with his feelings for Sirius and was also a little bit extremely angsty because even Remus Lupin had the major angst stage.
Little did Remus know, Lily also knew the basics of sign language so easily figured out what Sirius was smugly implying. She told this story in front of every single guest at Sirius and Remus' wedding.