| Ha Ha!
| Catchphrase Information
Ha Ha! (sometimes spelled Haw Haw!) is Nelson's catchphrase and distinctive laugh. Nelson says the laugh with the emphasis on the first "Ha," so it sounds like "HA-ha!"
Nelson usually uses the laugh when something bad happens to another character. Sometimes, after he uses the laugh, he says why he is laughing at the person. For example, he says, "Ha ha! Your dad's not handy!" to Bart after his ten-speed bike (which Homer had assembled) fell apart while Bart was riding it.
Sometimes Nelson laughs for so long at a time that his voice gets really tired and croaky.
Nelson seems to think that using the laugh gets him off the hook if he happens to cause something bad to happen to another person. For example, Nelson pranked Bart into falling out of a tree and used the laugh after Bart hit the ground. It turned out that Bart had broken his leg. When Milhouse pointed out that Bart was really hurt, Nelson protested, "I said 'Ha-ha'!"
Sometimes Nelson will start the laugh, and then partway through realize that the joke is actually on him, and the laugh comes out sounding like a question: "Ha-HA?" 
The Irish Nelson says "Har Har!"
When Bart jumps on the see-saw and the trash bag on the other side lands on him, Nelson says "See-Saw!" in the same way as "Ha Ha!".
Nelson trips up Facebook founder Mark Zuckerberg in a roller-skating rink. Zuckerberg falls and hurts himself and updates his status on Facebook to "is in intense pain". Nelson replies, posting "Haw Haw!"
Uses by Other Characters
- Mrs. Muntz has been known to use the laugh.
- Nelson laughed at a tall man driving a Volkswagen. The man got out of his car, confronted Nelson and lectured him. He then turned the tables on Nelson by making him walk down the street with his pants pulled down around his ankles while everyone in Springfield laughed at him.
- Bart was the only guest to attend Nelson's birthday party. The next day on the school bus, Nelson began treating Bart like his new best friend, much to Bart's discomfiture, and Lisa laughed at Bart. 
- When Springfield Elementary School had a medieval festival, Nelson laughed when Mrs. Krabappel announced that Martin Prince, Jr. would be the king. Mrs. Krabappel, for her part, said that Nelson would be one of the king's guards, and laughed at him when he looked shocked.
- When Bart had a string of pranks backfire (they ended up helping people instead of causing trouble), Reverend Lovejoy laughed at Bart when he grumbled that every time he tried to do evil, he ended up doing good.
- "I, (Annoyed Grunt)-bot"
- The Simpsons Movie
- "Bart of Darkness"
- "Loan-a Lisa"
- "500 Keys"
- "El Viaje Misterioso de Nuestro Jomer"
- "Margical History Tour"
- "Boy-Scoutz 'n the Hood"
- "Rome-Old and Juli-Eh"
- "Boy Meets Curl"
- "In the Name of the Grandfather"
- "Coming to Homerica"
- "The Debarted"
- "22 Short Films About Springfield"
- "The Haw-Hawed Couple"
- "The Father, the Son and the Holy Guest Star"