What do you think about using slang in your writing?
The official Rule is that you should avoid colloquialisms when you write. I can give you two good reasons for this.
1. They date your writing, just like any other popular reference. You can refer to some popular television show or catch-phrase, and all is well and good … for now. But a few years down the road? Not so much. Remember the Terminator’s “I’ll be back”? Or Bart Simpson’s “Ay, Carumba!”? Fonzie’s “Aaaaay”? Exactly. You remember them (or not), but if you used them in an article when they were popular, well, it won’t have aged very well.
2. They are unprofessional. Or rather, they make you sound unprofessional. Too many slang terms may make your readers think that you don’t know how to express yourself “correctly.” Colloquialisms by their very nature are casual.
That said, as with many (many) writing rules, this one relies on the context. So, when can you use slang?
1. When writing dialogue. No matter how correctly they speak, practically nobody completely avoids slang when having a conversation. You just expect less of it in a speech by a head of state than, say, a farmer from some isolated area. So, when writing dialogue, if your character would use more colorful language? Use it.
2. In casual writing. When writing a letter to a friend, you can and should write as naturally as you can. Because, again, unless you are a head of state, English professor, or someone in some other highly-literate line of work, chances are that you don’t speak like a textbook reads. Which means that, if you’re writing naturally, your writing isn’t going to be perfect. That might not be ideal when writing something official, but in an e-mail or a friendly note? By all means, go to town.