The episode begins with the idea that Archie is being unreasonable for refusing to accommodate Mike's hippie friends but as the plot continues to unfold it becomes more and more obvious that it is the hippies who are being unreasonable. Although Archie refuses to allow them to sleep together under his roof (as they are unmarried), he accepts (however grudgingly) every single proposal of compromise that Mike or Gloria or Edith can come up with, only for the hippie couple to then reject each one of them for entirely asinine reasons (never mind that they are guests in Archie's home). By the end, even Mike is fed up with them and sympathetic to Archie.
Cute Mute: Robin, who "only speaks with her eyes."
Elective Mute: Robin can speak, but she believes that "words are a waste of time", so she only speaks with facial expressions and gestures. She does this so insistently that Gloria, exasperated, eventually demands that she shut up already.