-Liz may like Jon's smile, but not that smile.
-Believing he should modify fundamental aspects of his behavior to please a woman.
-As long as he's bothering with an unnatural grin, to continue the grimace at home.
-Sharing any relationship problems, no matter how miniscule, with Garfield.
Garfield's Awesome Response:
We see characters with the same half-lidded expression nearly every day. It is the default facial expression for most Garfield characters, but it's amazing what a versatile utility player it is, and how subtly it can shade a character or moment. Garfield in panel one has to both look calm and normal next to Jon's frantic grinning. and express something like "I cannot feign too much interest, but as long as you're sitting here with a horrible Man Who Laughs look on your mug, and it's a given you're going to tell me anyway, we all might as well see how weird your explanation is." In panel two, the fourth-wall aimed pupils shift a millimeter: "You guys hear this?"
There's a world-wise truth to what Garfield says: being in love invariably causes pain, and it gets worse the harder you pretend to be happy all the time. Lest we mistake a lazy, intentional jerk for sage, ask what life experience Garfield has with romantic love.