The pink ghost is the most aggressive of the 4 enemies. This ghost represents smell/taste, and uses this to track you like a blood hound.
Like every ghost, this ghost is blind to every sense except the sense it represents and uses YOUR sense of smell and taste to locate you. It follows your trail by detecting where you have been breathing, so it will always eventually catch up to you and attack, even if your in a safe zone. You can hold your breath by pressing the middle mouse button and it wont be able to find you, hurt you, or be able to track you at any location you haven't breathed.
If it attacks you or begins to chase you, just hold your breath and get some distance, and it will lose track of you. However keep in mind you can only hold your breath for a limited time and moving around will increase your need for oxygen.
If it has continued success attacking you in a specific location, it will camp there and act as a sentry. Be especially careful of taking damage from it in tight hallways, stairs, or any of your favorite traffic areas.
Eating apples will also instantly tip it off to your location, but that does not mean you cant avoid it by following the steps above.
Keep in mind ghosts grow stronger, faster and more aggressive with each passing day.
Good luck!