Even that phrase, once clever, has now become a cliche. Yesterday's wit just isn't very fresh anymore. The idea of a cliche is a very interesting one to me, because--even though most people don't seem to think of it this way--a cliche is a temporal concept. An idea or phrase doesn't become tired until it is overused, and that takes time. Similarly, once everyone is tired of that phrase or idea, the cliche often sits fallow for some number of years, decades, centuries, whatever, and then re-emerges.
Everyone objects to cliches, especially in entertainment, and this seems to distress a lot of unpublished writers. "But I want to write a book about a group of children who go through a portal and defeat a dark lord!" they cry. I saw a rather interesting discussion on this at Rachel Vater's "Lit Agent X" blog. As part of her blog, she commonly critiques her queries, listing common themes (among other strangeness) that she finds among the ones she rejects.
The problem is, a lot of the themes that she identifies as cliches (midlife crisis, woman going out on her own, etc) are things that a lot of her blog readers seem to want to write about. Ms. Vater's point, which I think isn't clear to some of her blog readers, is that such an idea can't be the sole content of the book. One great idea is almost never enough to create an entire book from in the first place, and the problem is only compounded if the idea happens to be overdone or cliche at the time of the pitch (what is cliche at the time the book is pitched might well be different from what is cliche when the book is written).
The thing to focus on, then, is having sufficient sub-plots, minor themes, and character development. All of these things are what create context and depth, and these are what really make a book great. It's all well and good to have a cool central idea--"an historian goes back in time to see the effects of the plague," for instance. But Connie Willis' DOOMSDAY BOOK wouldn't have been both a hugo and nebula winner if it wasn't for the depth of the characters (the unforgettable Kivrin, Collin, Aunt Mary, Mr. Dunworthy, and so on), all the twists and turns in the narrative (no one knows exactly what has happened, everyone is operating on various wrong assumptions, and there is both a sense of dread and mystery that compels us to press on with baited breath), and the vividness of seeing these other places and times that Willis describes.
A lot of that might seem to have little to do with overall themes or ideas, but it actually does. If books were just a single strong idea, they would only need to be a few pages long to express that idea. The novel is in the story, the characters, the interplay of multiple ideas and scenarios. A 50-word abstract of a book has to let people understand that these necessary elements exist, and that there is something new and interesting going on.
While my original description of THE DOOMSDAY BOOK is not exactly cliche, it is two dimensional. Time travel has been something of a popular topic in science fiction for a while, and "person X goes to see time Y" is not a very original idea. What might be a more appropriate description for this great book: "An historian from the future goes back in time on a routine time travel expedition, and finds herself in a dangerous situation at the same time that a mysterious illness arises in her home time." That's still not the world's best description (I'm sure Willis herself has much better ones), but it highlights the intrigue and interest and genuine newness of her story.
So, to me the actual problem is not cliches themselves, but rather what a cliche implies: a two dimensional story that we've all heard before. No depth. No imagination, just somebody imitating something else they read and liked. Not a real writer, just a starry-eyed reader that perhaps wanted to read more of story X, and so decided to write story X all over again. At least, it sounds like those are the thoughts that pass through the agents' minds when they see something they feel is cliche. You need to show with your brief description that you are a real writer, and an original thinker. You can use cliche story elements in fresh new ways in your story, but when you do that in the proper way you wind up with something else entirely: an original story. Just make sure your one-liner does it justice.
P.S. - Another thing to remember is that when querying an agent you shouldn't be coy about your ending. This isn't a book jacket. You want to convey the uniqueness of your story, and if that requires spoiling some major plot twists or ending elements, then so be it. My description of the DOOMSDAY BOOK was less interesting because I didn't reveal said major plot twists (but it's not my place to spoil someone else's book).
It happens that my brief description for THE GUARDIAN that I use in query letters does spoil rather a lot, but that's life. If I didn't do that, I'd come off with a description that was cliche, confusing, or both. As it is, the description I'm using has piqued the interest of at least two agents and one professional writer (I guess I'll find out how much that's worth later this year).