Jennifer Tilly -- 76% Of My Celeb Friends Are Cheating Horndogs

Jennifer Tilly says most of her Hollywood friends are philanderers ... but adds the situation isn't as dire as Cameron Diaz thinks.

We got Jennifer last night -- sans poker-playing long-time partner Phil Laak -- and asked her what she thought of Cameron's observation ... everyone will be cheated on at some point in their life.

Jennifer says it's definitely more likely than not ... but sets the percentage at less than 100.