Crowd Song/Playing With

Basic Trope: A character starts singing, and several other people inexplicably join in.
 * Straight: Frank starts singing a song on the street which eventually leads the whole street singing that song.
 * Exaggerated:
 * Frank starts singing a very complex song with very elaborate words on the street and the whole city starts to sing in a perfect harmony.
 * Everyone on the entire planet joins in.
 * Justified:
 * People in the street are mind-controlled in a way that they must start singing a certain song if one person starts to sing it.
 * It's a music video, and the people are hired to sing it during a crowd scene while fist-pumping.
 * It's a popular song, and/or everyone there is in a choir.
 * Inverted: Everybody in the street is singing a song. Frank joins in and the rest of the crowd suddenly stop singing.
 * Subverted: It is revealed that the sing-along was preplanned (aka a "flashmob").
 * Double Subverted: It then revealed that the sing-along was planned for a different song.
 * Parodied: Frank starts singing, no-one joins in. Tom comes out singing the same song and everyone joins in.
 * Deconstructed: It's a train wreck... Most of these people have no real musical talent, none of them got a chance to rehearse, and a good number of them don't even know the words.
 * Reconstructed: ...Which is actually better.
 * Zig Zagged: The singing was pre-planned, for a different song, which everyone in the crowd spontaneously decides to do a medley of, at the end (or in the middle) of the song they were "supposed" to be singing.
 * Averted: Frank starts singing on the street, nobody joins in and he only gets a few "what the hell" looks.
 * Enforced: I love "Masters of the World". Let's get the ball rolling on a licence, and hire a few guys to belt it out along with Frank when he starts singing it! Ooh, even better, let's have the first few guys singing it actually be Sabaton!
 * Lampshaded: The lyrics are "Unplanned Musical Harmony La la la"
 * Invoked: "Quick! Distract everyone with a song!" "What?" "They can't help but join in."
 * Defied: "I am not singing with you." "Oh..." You're not either!"
 * Discussed: "Nice crowd song. Just like in the movies, too!."
 * Conversed: "That's a great crowd song. I think I'll join in."

Back to Crowd Song, where we can all sing along in harmony!