The female version of "Sausage Fest", "Bro-BQ", etc. Describes a party where the female to guy ratio is very high.
Partier 1: "Hey friend, what's the deal with the party you're at right now?"
Partier 2: "You've got to get over here ASAP, it's a complete Meow Mixer. I'm only one of five guys here, we're drowning in estrogen right meow."