The man, who is described as being in his 20s with short dark hair and a blue and beige jacket, verbally assaulted another person in front of members of the public and children in Minden Place on Saturday at around 14:45.
He was then said to have driven away in his black Citroen car.
The incident, which has been described as ‘disorderly conduct’ by Police, occurred on level two of the town car park.
Islanders who witnessed the incident or have any other information in relation to it are asked to contact Police on 612612 or anonymously via Crimestoppers on 0800 555 111.