What can we say? We’re suckers for punctuation jokes! Even better when they’re ambiguously dirty punctuation jokes.
Amanda seems to be smirking at Megan in the third panel. I’m not sure why, but I assume it is at her unadulterated love of the semicolon. Probably not, though.
MEGAN: I don't get why a semicolon wouldn't work there, because as far as I can see it would fit perfectly into the sentence; you might think it irrational to care about grammar this much,but when I know I'm right about grammar it drives me crazy to be told I'm wrong--what else could possibly make me so irate?
RICK: A period?