One that deserves a Poolitzer.
In marketing, the word "flushable" is kind of like the word "natural." No one regulates it, and it means just about nothing. You'll see flushable baby wipes or even flushable diapers, and their ads sometimes show the things harmlessly breaking apart after they go down the drain. But they need to be sturdier than toilet paper (which truly dissociates), so they use a lot of degradable plastics. In our plant's machinery, those products recombine into one giant plasticy mass, like The Blob. And that blobby monster has to be removed manually. I've personally had to sample this monster (that means grabbing a bit for testing, not licking and tasting it), and it was such a hard mass that I had to bash it with the sampling stick like a baseball bat to break it apart.
Another species of blobby monster comes from the fats, oils, and grease in wastewater, which we refer to by the appropriately blobby acronym FOG. You might regularly pour hot grease down the sink (say, from draining ground beef from the same tacos that give you diarrhea to flush later), and it's liquid when it rolls off your pan. But it loses temperature quickly and will solidify in your drains. So not only will you need a visit from a surly plumber in the not-too-distant future, some of the FOG makes its way to the sewers and builds up in interceptor lines. If the problem is bad enough, we all see terrible things we call "fatbergs," which are a nightmare for sewer maintenance.