When you displease someone, you disappoint them or make them unhappy. Your dog's loud barking at 5 AM is sure to displease your neighbors.
The prefix dis- is often used to signify the opposite of something, and displease is no exception: it means to do the opposite of pleasing someone. Your terrible grades will displease your parents and your teachers, not to mention you, and being served your least favorite foods at your birthday dinner will also displease you. Please has a Latin root, placere, "be acceptable, be liked, or be approved."