When a man tucks his penis and testicles between his legs and prevents them from springing forward by squeezing his legs together. This is done in order to imitate a vagina. If said man were to turn around and bend over, you would have a Fruit Bowl. The Taco is the opposite of the Ram, which is achieved by pulling the testicles up and partially over the penis.
"That guy in 'Silence of the Lambs' was totally doing the Taco in front of the mirror."