When we talk to our colleagues over lunch or coffee, it's much more candid. We don't hold back our feelings whether we want to rant or appreciate.
A manager/report appreciating each other in a formal setup may sound like, "You did a great job. Thank you for your hard work and support". When the same people talk about each other with others over a coffee, they sound more passionate. Example, "Dude, that person is super hard working and talented. I'm so glad they are on my team" or "I've had the best time working with my manager. The way they helped me gain confidence when I wasn't able to perform is incredible."
When I noticed the difference, I started passing on the compliments by quoting them. The candidness and unexpectedness of the appreciation have made folks quite happy. I have a hypothesis that it will also improve the relationship between the two individuals. A few of the responses I heard are, "I've been having such a difficult week. I was in the endless loop of self-doubt. Reading this made my way. Thank you for sharing this!", "I didn't know that someone actually learnt this from me. I'll start speaking more about my ways of working to help others."
We presume what we hear (about someone) must have been communicated to them already. This is especially relevant for high performers and folks higher on the ladder. Creating a culture of candid and generous appreciation is the ultimate goal. But it takes a while to build that. Till then, pass on the compliment and make someone's day!