Stands for 'Cunt to Cock Ratio' and refers to the ratio of women to men at a given event. It is rarely given as an actual number but its favourability is often discussed.
Person 1: "Hey, did you get any lovin' at Dave's party last night?"
Person 2: "Nah, his C2C ratio was shocking. Far too cock heavy."
Person 1: "What're you up to on Saturday night? Fancy coming to a housewarming party we're throwing?"
Person 2: "Depends. How's your C2C ratio looking?"
Person 1: "Very favourable. Amy's invited most of her gymnastics team along. We'll be knee deep."
Person 2: "Sold! What time's it kick off?"