If making ahead, prepare an ice-water bath fitted with a sieve; set aside.
Fill a large straight-sided skillet with 2 inches of water and bring to a boil. Add vinegar and return to a boil. Break one egg into a small heatproof bowl. Placing lip of bowl in the water, gently tip the bowl to slide egg carefully into pan. Use a large slotted spoon to fold the edges of the white over the egg, for a neater edge. Repeat with remaining eggs.
Cook until whites are just set but the yolks are still soft, they should still move around inside, 1 1/2 to 2 minutes. Lift out eggs with a slotted spoon or small mesh sieve and briefly rest on bread to allow eggs to drain. Trim edges with a knife for a prettier presentation before serving on toast, if desired, and seasoned with salt and pepper.
To make ahead, immediately place eggs in an ice-water bath to stop the cooking, then transfer to a bowl of cool water (it should just reach the tops of the eggs). If storing longer than an hour, place bowl in refrigerator (covered) for up to 24 hours. Reheat by briefly placing eggs in a pan of barely simmering water, just until warmed through. Serve on toast, if desired, seasoned with salt and pepper.