One of the best teachers I've ever had has a thing about grimaces. He says you should never use the word grimace in your writing because it doesn't mean anything. I would say a grimace is a frown caused by disgust. I looked it up in various dictionaries and they say a grimace is a facial expression, often ugly or contorted, that indicates disapproval, pain, etc. or a sharp facial contortion expressing pain, contempt, or disgust., etc. So, regarding grimaces, I guess: Caveat scriptor.
However, I think this points to a larger issue: the evolution of the english language. There's no question our language has evolved and is evolving over time. How much of this should we use in our writing? For example, in my work I would use "five finger discount", but not "index finger discount". Most people know the former but only a certain subset of folks know the latter (although we could probably figure it out!). Certainly, there are genre considerations here. YA should use a lot of slang. Techno- or geek-thrillers should also use a lot of jargon.
But, IMHO, we can go too far. 2MI can be 2M2H. IKR?
I think we should avoid text-messaging "words" in fiction.
What do you think?