He apologized and later stood by his statement, but it's the type of thing you just can't take back. Not unlike that proverbial tube of toothpaste, you just can't put it back in.
Rereading this, I keep wondering where one is supposed to put it (the tube?) back in to. The medicine cabinet? The box it came in? Seems more like a riddle than a proverb.
I searched for toothpaste+proverb, and the first hit was for for this craft project for Christian housewifes:
Words are like a tube of toothpaste. If used the right way, toothpaste helps clean our teeth and keep our mouth healthy. Words are the same way. If we use our words to cheer someone up and say nice, helpful things, our words can bring joy (health) to another person.
Sometimes we can get sloppy with our toothpaste. It can leak all over the cap and make an annoying mess. Same with our words.
It's all about Proverbs 12:18,
There is that speaketh rashly like the piercings of a sword; But the tongue of the wise is health.
I like it, "tongue of the wise." Healthy tongue, healthy teeth, I'm starting to see the connection. But I'm still not sure back into where I'm supposed to put the tube of toothpaste.