Gregory (played originally by Stephen Bogardus), who owns the country house and is deemed to be rather "saintly" by all of his friends, has been severely tested by Ramon's seduction of his young boyfriend Bobby. And what plays into Gregory's anger is also the fact that Ramon is lauded to be a hot young star in the modern dance world whereas Gregory's career as a star choreographer is on the wane.
The scene is about how such a sane and serene person can be pushed to the limit and do something so seemingly irrational and passionate (threatening to thrust Ramon's hand into the garbage disposal). I think because it's so outrageous and out of character, Ramon is ultimately not as threatened as he might be. But most importantly, he's the type of cocky young guy who gets off on the passions he arouses. And so he stays.