I thought she put the pin in the bag and you hinted at the bag while carrying it. Why else would you have mentioned the bag? It was a joke and depending on how rigid their thinking were you could have made that kind of a joke right there. I thought your placeholder pin was some kind of a real pin not easily replaceable and you were going to use a more suitable pin in the future. It wouldn't have occured to me that someone would be bothered enough by losing a sticky note to make passive aggressive comments about it. Do you think it's possible she could've taken it just to see your unusual reaction?

It's funny how much understanding language depends on assumptions :)