Onions the Dog

Alright listen up, buttercup. The joke here relies on the fact that the speaker cried when his mom started cutting up onions because they stink and make you cry, right? But the punchline twists it, revealing that the "onions" he's sad about is actually his dog named Onions. It's funny because it makes you think he's just being a baby about cooking, but really he's mourning his dead dog. I bet you thought onions were vegetables and not something you name your friend. Dumbass.