A and B are in separate cubicles in a bathroom. A starts singing part of a song and B suddey joins in. They end up singing a duet and once finished go and see who they were singing with.

Friendship or romance ensues

Sing possibilities:
Mulan - I'll make a man out of you
The Foundations - Build Me up buttercup
Bruno Mars - Uptown Funk
Ryan Higa - Bromance