sauce
Explanation
This is a short comic strip set in what appears to be a pizza restaurant. A delivery person or customer has dropped the pizza and says: "Oh no, I dropped the pizza. I'll have to get a new one and come back." They then note: "I don't have her number. I'll have to leave a note." But then: "Wait, I don't have a pen either. But... the sauce!"
The final panel shows the person dramatically declaring "I'll be back" while apparently using pizza sauce to write a message -- striking a dramatic pose reminiscent of an action hero, specifically evoking Arnold Schwarzenegger's iconic Terminator line.
The joke is a simple escalating-absurdity gag. What starts as a mundane delivery problem (dropped pizza) escalates through a series of missing tools (no phone number, no pen) until the character arrives at the ridiculous solution of using pizza sauce as writing material. The humor comes from the contrast between the extremely low-stakes situation (a dropped pizza) and the over-the-top dramatic framing of the solution, complete with the heroic pose and action-movie catchphrase.
The comic plays on the idea of making do with what you have, taken to an absurd extreme. The Terminator reference elevates a minor food-service mishap to the level of an epic action-movie moment, which is inherently funny because of how wildly disproportionate the dramatic energy is to the actual situation.