It is presumably two or three scoops of vanilla ice cream with chocolate sauce "hair" and a banana and cherry hat. It has banana and cherry arms and three chocolate (or other candy) buttons for eyes and a nose with a big red licorice smile.
SpongeBob and Patrick were eating them very quickly and rapidly, which caused them to get a big ice-cream headache. All the mess that SpongeBob and Patrick made flew onto the Goofy Goober waiter.
This may be SpongeBob and Patrick's favorite ice cream of all time considering they ate large amounts of it.
It was mentioned in the episode "The Clash of Triton" by SpongeBob; however, he pronounced it as "Gooberry," not "Gooberberry." Harold also asked for one at the ice cream shop in "Porous Pockets." However, he asked for extra nuts, and there are zero on the sundae. However, it is possible that the nuts are either optional or inside the sundae.