It is strawberry ice cream topped with a huge amount of caramel syrup and a cherry on top.
Role in episode
Patrick orders the caramel sundae while he is trying to help SpongeBob cope with his sun bleached problem. As he goes to eat it, he notices SpongeBob looking brown through the caramel reflection, which gives Patrick an idea: He throws the sundae onto SpongeBob and covers him with the caramel syrup to make him appear tanned so he can attend Craig Mammalton's party. However, later on it comes off and reveals that SpongeBob is sun bleached.