Our 2 1/2 year old daughter tends to stuff her mouth completely full when she eats, and then will open her mouth for another spoonful. We often have to say, "Swallow what's in your mouth, then you can have some more."
Another favorite game of hers is to fill her mouth with whatever we've given her in a sippy cup, and then let it drain out.
She was doing this last night with her tea, so we warned her we'd take it away if she didn't stop. Alas, it came to be, and we gave her a cup of water instead. Though she initially appeared to have learned her lesson by losing the tea (her favorite), a short while later she resumed spitting out the water, and I said to her:
"Honey, good girls don't spit, they swallow."
The nanosecond those words left my mouth, I couldn't believe I'd said that. I even slapped my forehead and said, "I can't believe I said that."
It took my wife a good 10 minutes to stop laughing hard enough so she could call all her friends and tell them.