What does "Break it and shake it" mean?

If you hear a waitress say "Break it and shake it" at a diner or restaurant, it's just another way to say "To add an egg to a drink." It was especially popular in early diners to add an egg to milkshakes. There are hundreds of other popular diner lingo phrases - to learn more, check out the links below or browse the rest of our restaurant slang dictionary.