Chummy Joes are a food item sold at the Chum Bucket that appear in the episode "Mermaid Man vs. SpongeBob."
They consist of two sesame seed buns with chum in between them. The way the chum is put in the buns makes it look messy.
Role in episode
At the end of the episode, Plankton tells the fish at the Chum Bucket that he would serve Chummy Joes to them, but they had already left for the Krusty Krab.