A. If I were Jon's date, I would have him arrested for lapels that stick up over his shoulders.
B. Garfield, I guess, is making fun of Jon for knowing he's dull. But really, it's Jon's self-awareness that makes his plight that much more horrible... and funny.
C. Once again, though Jon's date is trying to indicate something is wrong with his personality, all she ends up doing is demonstrating her possible insanity. You're not supposed to think about it, to make the joke work, but in the reality of the strip, the woman actually did call the police and tell them her date was boring. That means she is a crazy person.