Maybe when they're stuck in the garbage hole, and they hear a noise from under the water, and Han says "it IS worse", but then quickly replies to Luke's concern "yea, your imagination, kid".

Either a brilliant form of subtle characterization (he's grumpy and doesn't mind pointing out when things look bad, but at the same time wants to appear in control and above it all), or... a sloppy form of crude characterization (insert a grumpy line here, insert a hollywood skeptic line there).

His delivery makes me go for the former :)

EDIT: FORMER, FORMER... I meant FORMER! :D