Toothpaste
Toothpaste
[Cueball, holding his arms out, is talking to Megan.] Cueball: I can't believe she said that. Cueball: She apologized, but you can't put the toothpaste back in the tube.
[Megan holds a hand, palm up, out towards Cueball as she replies.] Megan: Sure you can; it's easy. You just put your mouth over the opening.
[Finally they stand straight talking.] Cueball: Well, that's the worst thing you've ever said. Megan: Sorry, I can take it back. It's just like- Cueball: No!

Cueball is telling Megan about his friend. He indicates that she said something shocking and probably hurtful. He then states that even though she tried to apologize it was too late, the words had been said and it cannot be taken back.
He uses a phrase to underline this: You can't put the toothpaste back in the tube.
Putting toothpaste back in its tube is often used as an analogy for something irreversible, such as how you can't undo speaking. Megan, however, rejects this assertion and says that you actually can put toothpaste back in its tube, which is certainly possible in some cases. There are many ways to do this, and none of them are recommendable if the toothpaste has come into contact with something non-sterile.  But she chooses a particular nasty one where she would blow the paste in her mouth back into the tube. This is obviously much more unsanitary than simply returning unused toothpaste to the tube, which someone might reasonably want to do after squeezing out more than they wanted.
Cueball is so disgusted by this suggestion that he states that Megan's suggestion is the worst thing she has ever said.
The joke then comes when Megan assumes that Cueball's original analogy still holds, that taking words back is like putting toothpaste back in to the tube. So therefore she can actually unsay something. She starts to say exactly what Cueball's other friend did "Sorry, I can take it back". But then she says, "It's just like--", and was presumably about to continue,  "--putting toothpaste back in the tube" (or perhaps, since it's Megan, was going to give a new analogy that was even worse). However, Cueball forcefully interrupts her, because the idea of putting toothpaste back in the tube now evokes the distasteful mental image of Megan blowing used toothpaste back into the tube.
Toothpaste is normally loaded into the tube from the back, before it is crimped shut. However, it should technically be possible to push an extruded amount of paste back in from the front by wrapping one's lips around the whole front of the tube and blowing the paste you have in your mouth back in. This positive pressure can re-inflate the tube the same way one blows up a balloon. However, blowing the toothpaste back into the tube would be highly unsanitary, and as the main purpose of toothpaste is to clean teeth, the end result is both counterproductive and disgusting. [ citation needed ] In some cases paste coming out of a tube will be sucked back in if the pressure is released. Such containers would probably be able to suck toothpaste back in, if it was still lying on the toothbrush in one blob (or on the table/in the sink if dropped). As above mentioned this would be unsanitary as germs etc. could get back inside the tube, where the paste is supposed to be clean.
The title text spoofs a common line found in toothpaste commercials: "9 out of 10 dentists recommend using our brand." This statement is very easily manipulated through any number of basic marketing tactics (such as only asking 9 dentists, whom are all paid handsomely), and its ubiquity lends it to spoofing. In this case, it's spoofed by saying that nine out of ten dentists are dis satisfied with Megan's approach (or with Randall and his ideas, as it is usually he who speaks in the title text; if it refers to Randall himself it is reminiscent of all the conferences he has been banned from ) and have banned the toothpaste spitter from their offices.
It may actually say more about any dental establishment that does not disapprove of what Megan apparently is not just theorizing about doing - but maybe they are disapproving too, just not considering it bad enough to ban her from office.
[Cueball, holding his arms out, is talking to Megan.] Cueball: I can't believe she said that. Cueball: She apologized, but you can't put the toothpaste back in the tube.
[Megan holds a hand, palm up, out towards Cueball as she replies.] Megan: Sure you can; it's easy. You just put your mouth over the opening.
[Finally they stand straight talking.] Cueball: Well, that's the worst thing you've ever said. Megan: Sorry, I can take it back. It's just like- Cueball: No!
