Hard to remember all original reactions to the original 2 games - after all, it has been 17-18 years. I rarely react the same way when seeing it a second time - it's the shock of a funny bit the first go round that can catch you off guard. But here's a couple I do recall laughing out loud to:
With Stan on the dock, looking at the sea monkey, with the shooting star and "I think we're having a real moment here"
Near the end, by the river of lava: "How did you get in here without using the head?" (and the reaction from the crew, alternatively Herman)
On Kate's ship: "What did you do, order this ship out of the back of a comic book?" and "This ship is so small the rats leaving it are humpbacked" - and the retort: "The guy who writes your lines is as funny as your tailor"
(oh, by the way, another one in that scene is "I've seen COFFEE CUPS bigger than this ship" - another "he's really in an amusement-park" reference?)