Hobgoblin

The Hobgoblin is one of the creatures Bart and Homer found inside their pit trap in their attempt to catch the Leprechaun.

History
When Homer and Bart checked the trap the morning after digging and baiting it, they found several forest creatures inside it. Bart started pulling them out one by one, naming each one before tossing it aside. When Bart got to the Hobgoblin, he said "Goblin", and the Hobgoblin angrily corrected him: "That's Hobgoblin!" Bart said "Sorry", tossed the Hobgoblin aside, and moved on to the next creature. Soon after that, he got to the Leprechaun.

The Hobgoblin later attended the wedding of the Leprechaun and the Gypsy.

Behind the Laughter
In traditional folklore, while it's possible for and  to appear similar to each other, Hobgoblins are generally more humanlike in appearance. Also, their behavior is completely different: While Hobgoblins can actually be helpful to people and generally confine their mischief to practical jokes, Goblins have a nastier streak and are much more malicious. Bart's confusing the Hobgoblin with a Goblin is understandable, but the Hobgoblin's indignation at being misidentified is even more understandable.