Originally I was going to make this about awesome concert experiences but, I'm just going to widen the topic a bit so everyone can participate.
What made me think of this thread was I was remembering the time that I watched Eddie Vedder and Dave Grohl in unision, sing happy birthday to Joan Jett on stage- along with an audience of 15k people (minimum). I honestly don't know how many people were there but it was the biggest concert I've ever been to let's put it that way. It was on a beach.
And then they sang some songs together, they aren't recorded songs or anything they've done together, so it was a rare moment that just the attendees of this concert got to witness.
Oh yeah and I shook J.Cole's hand once lol like standing face to face. It was after a concert I just kind of ran into him lol