These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
"Funny Aneurysm" Moment: Winthorpe saying "It's kill or be killed" and "Nothing you've seen in your life can prepare you for the unbridled carnage you're about to witness" as he and Billy enter the World Trade Center for the climax.
And it had another nasty connotation much quicker, given the deaths of Vic Morrow and two child actors during filming of John Landis' segment of the Twilight Zone movie.
Genius Bonus: The music theme of Trading Places is the Overture to The Marriage of Figaro. The Wolfgang Amadeus Mozart opera is about a servant who outwits his master. Also, the movie's title has a double meaning. It not only refers to the main plot in which two men are forced to switch lives, but also to the climax, which plays out at the New York Mercantile Exchange: a trading place.
The climax itself falls in this category. Very few movies stage an ending at a stock exchange, and the plan executed by Winthorpe and Valentine is brilliantly simple in light of the public finance principles behind it. Even a child or someone with no knowledge of stocks at all would be able to understand "how can the price be going down?" means the villains are losing their money.
Moral Event Horizon: While the Dukes had slowly gained their way up into this territory already, the Bathroom Stall of Overheard Insults scene depicts them not only gloating about switching the lives of two men (and thus destroying the life of one) over a bet for one dollar, but also deciding to leave both men homeless and worse off than before (they have no interest in rescuing Winthorpe from the gutter and intend to get rid of Valentine, adding a racial slur just for a final touch). From this point their immensely satisfying downfall starts to take place.
Older Than They Think: The premise of Trading Places, where two wealthy businessmen bet over whether heredity or environment makes a gentleman, and proving it by taking a bum off the street and making him sophisticated, was previously tackled in The Three Stooges short "Hoi Polloi".
And funnily enough, nature rather than nurture wins out in that one.
Older than that: Mark Twain had a short story about two rich men betting on whether or not a bum would benefit if bearing only a single 10,000 pound note.
Older than THAT, even. The story bears strong similarities to the Book of Job (God and the Devil make a bet about whether Job will stay faithful when God ruins his life in every conceivable way), right down to them just doing it because they were bored. Job is probably the inspiration for all stories of this type, come to think of it.
The Plot Writes Real Life: In 2010, the "Eddie Murphy Rule" was proposed to prevent commodities traders from using nonpublic information, such as the Department of Agriculture crop report depicted in the film, to corner the market in the same way as shown in the movie.
Values Resonance: The themes of how wealth, or the lack of it, affect the character of people, and of course the cautionary tale of people (attempting) to ruin lives to turn a profit probably make the movie a bit more poignant in the wake of the Recession. Also Some Anvils Need to Be Dropped.
Vindicated by Cable: The movie was a box office hit, but might have faded into obscurity, if not for constant replaying on cable around Christmas-time, even though the movie is not inherently a "Christmas movie."