I looked up the Yahoo Dictionary of Hong Kong, and it tells me the word I was looking for is this: "Ha Ha Point".
Yahoo Dictionary says "Ha Ha Point" is a network language that means "punch line", which is usually the part of a joke that makes you laugh.
I get that "Ha Ha" mimics the sound of laughter and that a "point" to which you can't help but laugh is the result of the punch line, but is "Ha Ha Point" English? Is it really a network language claimed by Yahoo Dictionary? To me this "Ha Ha Point" is too strange to be valid.