I learned to take the battery out of my alarm clock before traveling by Greyhound. I have a screaming meanie 220 alarm clock that's 110 dbl of loud and it went off in the D.C. terminal about 3 blocks from the U.S. Capital building. I had set my bag down and went to get someting to eat and the damn thing went off. Before I could get to it two guards with .357 Magnums drawn were yelling and running my way. I had to open the bag REAL REAL SLOW and show them what it was. I almost went to jail over an alarm clock, so now i take the battery out of it. Hard lesson learned but at least I didn't go to jail.
It's because once you get the toothpaste out of the tube, you can never get it back in. Can you imagine the mess you'd make in the aircraft restroom with 8 or 10 ounces of toothpaste?
Razor blades, on the other hand, might give you a close shave, but a few whiskers won't clog the aircraft sink.