When it comes to your novel, though, there are three good reasons to avoid pop-culture references.
- It dates you--quickly. (Also a problem for people using technology references in novels)
As you're probably well aware, in this age of the Internet, trends are like meteors flashing brightly on their way through the earth's atmosphere. They last just a moment. If you want your novel to endure, to really feel timeless, don't have your characters sitting down to season four of The Sopranos (or worse, Magnum PI!). Unless your story is clearly supposed to be rooted in that time period, you're limiting yourself.
- Not everyone will get it.
The last thing you want to do is alienate your readers. If you spend time making references (no matter how witty) to a show or meme or trend that your readers haven't seen or heard of (or that they've already forgotten about!), you're going to lose those readers, confuse them, or cause them to come out of the story in order to figure out what you're talking about. That's the last thing you want! Do whatever you can to keep your readers connected to the characters, invested in the story, and turning the pages.
- It's unoriginal.
Seriously. It's your world, even if you've set the story on modern-day Earth. Take a few minutes to imagine your own version of the soda, tennis shoes, or TV show that your characters are referring to! Own your world and show off that brilliant imaginative mind. (Bonus; No one else will have the same reference in their novel, so yours will stand out!)
So next time you're tempted to slip in a witty line about Downton Abbey or New Coke, stop! And use your imagination to create references that are an organic part of your own world, a world your readers will love and won't want to leave.