TV
It’s the non-relationship drink of choice. It’s not a date, it’s a caffeinated beverage. Okay, sure, it’s hot and bitter like a relationship that way, but…
— Willow · Buffy the Vampire Slayer

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Willow insists coffee is just a drink, not a date. She protests a bit too much, then admits it's hot and bitter like a relationship. The joke is that half-concession, where her defence of casualness accidentally describes romance.
Context reviewed