The idea is that an already successful barber shop takes their practice somewhere new, usually a clothes shop or a shopping centre, to deliver on-the-spot trims.
However, gym-goers were left confused when two men starting their own express pop-up barbers in a Sheffield gym on Monday.
Twitter user Em Hunt posted the bizarre footage to Twitter in a video which has been thousands of times.
In the video, one man can be seen crouched over in the gym's lobby whilst another man in a hat takes a shazer to his head.
A pile of hair can be seen on the floor as the man hurriedly shaves away his 'customer's' hair.
Em said that the men 'literally came into the gym, plugged in their shaver and set up a pop-up barbers'.
In pictures posted afterwards, the man can be seen leaving the gym with his hair in his hands and a completely bald head.
She said: "He literally picked it all up, said 'cheers' and left".