Another example of the last-panel turnabout joke, this time involving a chase. Be warned: a lot of these are coming up. It's funny how this joke, about "being hot" would be considered flirtatious today. I like the exclamation point above Patty's head in the third panel, a way to show surprise without having it register on the character's face.
The punchline from Charlie Brown, "I get my laughs," is rather meta. The formula on this style of joke is pretty strict, and the ultimate humor relies on coming up with something for the joking character to say in reference to his motive in the last panel. Schulz used them enough that he must have had a hard time coming up with fresh punchlines for these sequences.