Haha, it's kind of an inside joke. When they rehearse, they usually don't rehearse, they just chill in their rehearsal space.
The story behind the toaster is that the girl and the fourth dude that isn't visible on the photo used to stay in the rehearsal space really late, so the often slept there. Now, they also needed food, so they started buying bread and got themselves a toaster
Most people probably didn't get it, only a handful did, but those who did, including me, thought it was hilarious