Plot hole: Throughout the series, Sandy always refers to Daria as "Quinn's cousin" or "that girl that lives with Quinn" or other random titles for Daria (not knowing that Daria is Quinn's sister). Although Quinn admits to Sandy that Daria is really her sister in one of the last episodes of the final season, in this first episode of the series, Sandy is in the crowd watching Daria give a speech and Daria reveals to everyone Quinn is her sister (embarrassing Quinn). Sandy should already know they're sisters.
The New Kid - S2-E7
Plot hole: In the season two episode 'The New Kid,' Daria and Jane are discussing The New Kid in gym class when a girl takes a nasty spill from a trampoline. Later, Daria and The New Kid are heard remarking about photos taken of that particular fall despite there having been no photographers present.
Answer: "Mack Daddy" was a 90s phrase meaning "Ladies man," and Mack simply doesn't like the stupid nickname.
Brian Katcher