ballroom blitz

(n) A riot in a nightclub or other performance space in which the audience physically assaults the performer(s), typically by throwing things at them.

"And the man in the back said "Everyone attack!" and it turned into a ballroom blitz." -- "The Ballroom Blitz," song by Nicky Chinn and Mike Chapman

lobby ladrone

A thief of packages, mail, etc., from apartment building lobbies and other common areas. Identical to "porch pirate" but targets multifamily buildings rather than single-family homes. ("Ladrone" is Spanish for thief.)

Where's that package Amazon said they delivered? Goddamn lobby ladrones struck again!