nerd-jokes
Explanation
The Joke
A man tells his girlfriend Sally that he wants to break up because he "just can't take any more of your nerd jokes." Sally responds defensively: "There were some that you liked." He challenges her: "Oh yeah? Be specific." She repeats her answer -- "There were some that you liked" -- but this time the word "specific" is annotated with its physics unit: kg/m cubed (kilograms per cubic meter), which is the SI unit for density, not "specific" anything. The joke is that "specific" in physics can refer to a quantity measured per unit mass or volume (such as specific gravity, specific heat), and density (kg/m cubed) is the measure of how much mass is in a given volume -- essentially a "specific" measurement.
Sally has weaponized the breakup conversation itself as a vehicle for yet another nerd joke. When he asks her to "be specific," she takes the word "specific" literally in its scientific sense and provides the units for density, thereby proving his point that she cannot stop making nerd jokes even in the most serious of moments.
The Humor
The humor operates on two levels. On the surface, it is a pun on the word "specific" -- he means "give me examples" but she interprets it as a physics term. On a deeper level, the comic is self-referentially funny because Sally's inability to stop making nerd jokes, even during a breakup triggered by her nerd jokes, perfectly validates her boyfriend's complaint. She is literally proving his point in real time. The visual deadpan of Sally's expression -- completely unfazed by the emotional gravity of the situation, glasses reflecting blankly -- sells the character perfectly.
References
In physics, "specific" quantities are those expressed per unit mass (e.g., specific heat capacity in J/(kg*K)). Density, measured in kg/m cubed, describes mass per unit volume. Sally is making a pun by interpreting "be specific" as a request for a unit of measurement.