Divide the crowd into 3 or 4 groups. Give a topic or theme (such as songs mentioning a colour or a boy/girl’s name). Then have each group, in order around the room, sing the appropriate line that has the theme from the song. So if the chosen theme was colours one team might sing “We all live in a yellow submarine” while the next team might sing “There’ll be bluebirds over, The white cliffs of Dover.” and the next “Ninety-nine red balloons go by” and so on.
No repeats are allowed and the winners are the last group left able to come up with a related song line.