Endo-fundic is a word-set 📝John Zdanowski and his friends invented in college: an endofundic person sucks the fun out of a gathering, while an exofundic person contributes fun to it.
The pair is modeled on the chemistry of endothermic and exothermic reactions, which absorb and release heat. In the joke, fun plays the part of heat: the exofundic guest gives energy to a get-together, and the endofundic guest draws it away. The words describe a person's effect on a group's mood rather than their personality in general.
John recalled the coinage after reading 📝Brian Swichkow's memo on 📝fun-ctional, a word for contributing to a larger whole while providing equal or greater enjoyment, sometimes called productive play. Where fun-ctional describes fun that also gets something done, endofundic and exofundic describe whether a person adds fun to a gathering or subtracts it.
After reading Brian Swichkow's fun-ctional memo, I was reminded of a word-set we'd invented in college.