I was laughing at him laughing

Especially when the country represented by that flag probably no longer existed.

He laughed because of how little a thing it was planting a small flag 320 light-years from Earth 2,000 years after when they left.

Plus Taylor believed that everything they had known on Earth was now "dust".

I took it as Taylor thinking that the American flag (or anything from Earth) would be meaningless to whatever life (if any) they found on the planet. Plus, usually, when a flag is put up, it shows possession of the area which wasnt worth the distance they went through.

Affirmative.

That's why Taylor laughs at the flag but it still sets up the irony of the ending.

I also took it that Taylor was amused at the futility of Landon representing a civilization that was "long since dead and buried".

No I think that it is meant to be more ironic. Early in the film Taylor laughs at the flag, a symbol of America. At the end of the film he is anguished at the sight of another symbol of America, the statue.

Does the flag qualify as the first subtle hint at the grand climactic twist?

That's what I thought too. It seemed dubbed or at a minimum enhanced. Why should he laugh so hysterically?
-In my mind, Christopher Reeve will always be Superman.-

Taylor had just told Landon that he has to let go of everything he knew - it's all gone. They (think) they're on a different planet lightyears away from Earth and it's 2,000 years later..obviously Taylor is laughing at Landon still holding on to a past identity.
Pretty obvious from watching the film that the laugh was dubbed in post-production. Might not have even been Heston's laugh. It was likely dubbed for greater effect. And with the way the camera zooms, it's almost like something from a horror film. I don't necessarily think it was added for comedic affect. It just makes a profound, perhaps even unsettling, statement

Yah, every lousy actor should win so many awards.

Charlton Heston was just a pretty lousy actor.

That scene seemed something out of a spoof film, but I liked it. It was just too funny.
Life is like a beautiful melody, only the lyrics are messed up.

Nice words, you really stuck it to the commie up above. USA! USA! USA!

SPQR
"Maybe it's another dimension. Or, you know, just really deep." Needy

Because when little Tommy looks up in to the sky at night, he knows that somewhere, light-years from home, stands an American, with the courage and determination to raise the stars and stripes and bring freedom across the galaxy.
God Bless the United States of America
(f/22-A's fly overhead while national anthem plays)

Because it was so stupid in so many ways, which have been elucidated on this thread. Here they were on another planet hundreds of light years away (or so they thought), 2,000 years after they had set off, and this guy was planting the flag of a country that was extremely unlikely to still exist, and even if it did still exist nobody would give a damn because (again, as far as they knew at the time) it was a small portion of some speck of a planet far off in the universe. Like, imagine if at this very moment, right now as you're reading this, three dudes are appearing on some faraway planet and one of them is planting a flag of the Roman Republic. Think about the absurdity of that for a second.
And in any case, regardless of whether the US would still exist or not, they were just three guys on some unknown planet so how absurd is it to still care about countries anyway? Showing up on another planet is a great opportunity to see how stupid patriotism is and scrap the whole concept of countries, an artificial division between human beings. What would be the point of perpetuating that concept on another planet?
I thought the laugh was hilarious and really perfectly expressed just how absurd planting that flag was, as was the sentiment behind it. I'd have laughed too, and exactly the way he did.
"The people, and the people alone, are the motive force in the making of world history."
Mao

Taylor was probably just letting off steam. He did find the flag-planting humorous, and was just letting it all out. It was one of the few comic-relief scenes in the movie.

This message has been deleted.

To be fair, I would have laughed like Heston. On top of that I would have added 'You fv
You are entitled to my opinion, whether you want it or not!!

Yes, quite a maniacal laugh that felt totally overdone and out of place. I was sorry that they hadn't the forethought to give Heston a Professor Hinkle-esque mustache so he could twirl it.
Lie still. I've never done this before; and there will
be blood.

True James. This adds to the ridiculousness in Taylor's eyes!
You are entitled to my opinion, whether you want it or not!!