smile point ，lough point；smile dot；lough dot？
The part of a joke that makes everyone laugh or delivers the "punch"
eg："Oh man, the punchline of that joke made me piss my pants"
the words at the end of a joke or story that make it funny, surprising, etc.
简单说：He laughs too easily.
复杂说：He has an uncontrollable urge to laugh.