No, not the people who take care of your pet. "Groomers" is a temporary label (I'm open to suggestions for alternatives in the comments field) for those people who are the exact opposite of obnoxious people who insist on spoiling books, movies, et cetera for people who haven't seen/read them yet. (Obviously, this has been a bit in the public consciousness lately, due to 'Harry Potter and the Deathly Hallows'.) And I'll admit, I'm starting to find them every bit as obnoxious as spoilers these days. (And I stress, I do find malicious spoilers very annoying. Telling people who don't want to know, just because you get a kick out of being a jerk, is cruel and there's no getting around it.)
By "exact opposite", I mean that while a spoiler wants to make sure everyone knows the twist to the film/book/whatever, whether they want to know ahead of time or not, the groomer has a fanatical obsession with making sure that nobody finds out the twist ahead of time, even if they don't care or actively want to find out early, because making sure they experience the "de-flowering" of learning the twist as the writer intended is absolutely vital to enjoying the experience.
Obviously, you're more likely to find grooming in the creative end of the spectrum, while spoilers tend to be consumers of entertainment. Some prominent and (relatively) recent examples would be J.K. Rowling's anger at book reviews of the seventh Harry Potter book, Peter David's (probably joking) attempt to relabel spoilers as "ruiners", DC's solicitation to retailers of two non-existent issues of the Flash in order to conceal the impending death of the character, Marvel's solicitation of false covers of comics to conceal the ending of 'Civil War' (and, some years previous, the return of Colossus)...heck, you could go on forever. (One more, which I think actually worked well, would be the spreading of misinformation about the upcoming 'Thunderbolts' comic in order to conceal the fact that the team was really the Masters of Evil. This, I think, was where the idea really took root for the comics industry.)
So when does a writer go overboard? When does a natural desire to allow the story to unfold at its own pace become a maddened quest to thwart the dreaded spoilers? For me, I'd say it's the point at which you become willing to mislead your own audience, when you decide to take the very important (to storytelling) art of misdirection outside of the story and into real life. It's one thing to plant a red herring in your story; fiction is by definition a lie, and that's only a problem if it's not a consistent one. But lying in real life isn't a good habit to get into, and it's certainly not a good thing to do when a) you're doing it in such a way that you will, by definition, be caught in a lie by anyone who reads your story, and b) you're doing it over something as trivial as whether a person knows your plot twist ahead of time. ('Thunderbolts' remains an exception to me, because I thought of it as a piece of performance art. You, the reader, were being put into the world of the Marvel public, believing the T-Bolts to be new, shining, untarnished heroes that had just come onto the scene. Finding out that they were the Masters of Evil was almost an audience participation moment, not just a plot twist.)
But ultimately, as I say, the plot twist is trivial--that's the truly important thing to keep in mind. If your story really is genuinely spoiled by spoilers, it probably wasn't very good in the first place. A good plot twist, an actual authentic amazing plot twist, is designed to be read twice--once when you don't know the secret, and again when you do. Being "spoiled" just moves you ahead to the second stage, it doesn't actually spoil it. If you've crafted a good story, that will stand up even years after everyone knows that 'Rosebud' is the sled. (Oh, sorry. That should have had spoilers.) If you're throwing a surprise party, while you don't want to lose the "surprise", you should remember that the important part is the "party".