"Drama includes all human behavior. Nice people being nice to each other is a bloody bore. Do none of your friends ever say things that may be offensive or unkind?"
Absolutely agreed, but I guess it's a question of degree as to whether the bad behavior of the characters seems organic rather than included for effect, and also what's interesting rather than off-putting.
"As for the garbage disposal, he doesn’t do anything, he simply threatens."
That's an example of what I mean. If you were at a country house with someone and he threatened -- only threatened -- to shove your hand down a garbage disposal, wouldn't you leave immediately and NEVER see him again? But I don't think that's what happens in the play.