[maqp]

Some DJs use this principle when they need a hacky stage mic. They plug their headphones to the mixer's mic input, and shout to the speaker element.

[lelandfe]

E.g. this music video (evoking old Just Jam sets): https://www.youtube.com/watch?v=_xQKWnvtg6c

To really take it to that next level, snap the headphones in half when you get up on stage for a lollipop. Even seen one bring a corded phone and cradle to a set.