When I was in high school I loved the word juxtaposition. I think I used it in every single AP English essay I ever wrote. Dictionary.com says: an act or instance of placing close together or side by side, esp. for comparison or contrast. I think of it more like, Awesome Stuff next to Differently Awesome Stuff = Literary Awesomeness. Dude, you can totally see why I rocked 5s on those AP exams.
If you're confused, all you need to know is: Stephen Colbert, and polar bears.
I am so glad the following interview is online for you to see. TV often makes me chuckle out loud, but this one had me nearly horizontal with laughter. And to break it down Jane Espenson-style and figure out why it's funny: I think it's the juxtaposition of a cute little polar bear puppet with the ridiculously harsh stuff coming out of Stephen's mouth.
The fact that he's a comic genius is also convenient.