Best definition
When someone is waterproof, it means solid. It has to do with leaking a secret or snitching. One who is waterproof will not leak any information to someone else.
1.Come on, tell me. You know I am waterproof.

2. “Why did you tell that kid?” “Don’t worry he’s waterproof”
waterproof: define #2
a face that doesn’t require make-up
Tommy: Did you see that girl over there?

Ben: Yeah, she’s a water-proof babe.
waterproof: define #3
When a member of the female species has all her bodily cavities filled with penises, fingers and/or dildos she is said to be waterproof.
Mischa Barton had Ron Jeremys cock in her pussy, Stephen St Croix snake crawling in her rectum and John Holmes dick in her mouth, and was thus waterproof when Rocco Sinfredi sprayed her with Pimp-juice.