Perhaps for you it is nails on a chalkboard, or maybe the snap of bubblegum, or even the sound of a particular person's voice.
Naming the "harshest sound in the world" seems like it would be a subjective matter, but scientists say they have pinpointed the sound that qualifies for the moniker.
According to a research study by a team at the University of Newcastle, the harshest sound in the world is a knife against glass.
The team examined brain activity in a group of volunteers, who listened to 74 recorded sounds under an MRI machine and ranked each experience, according to ABC News. The 13 subjects found the sound of a fork against glass to be the second worst sound.
The group found that sounds with frequencies of 2000-5000 Hz were the most disagreeable.
The MRI scans showed that these sounds increased blood flow in the brain's auditory cortex, which processes sounds, as well as triggers the amygdala, a primitive part of the brain that processes our emotional responses, according to MSN.
While it's hard to imagine a study like this ever having a purpose beyond finding a better torture technique, Tim Griffiths, the study's co-author, said, "The new finding in this study is to precisely define the loop between the auditory cortex and the amygdala."
In the mood for a bit of masochism? Take a listen to what scientists say is the harshest sound on Earth.