A sexual act in which a male penetrates an extremely large female from behind. To complete the act, he must lift his legs off the ground, using only the giraffe-sized female's body to support his weight. This will cause the female to become very rowdy, and likely will cause her to start running.
To qualify as a giraffe, the female must be at least 5 ft 10 in tall and taller than the man. The only exception is if the man is a midget. If he is a midget, she must only be 1 ft taller than him regardless of his height.
Disclaimer: Do not try this at home unless under the supervision of trained professionals such as Gary Coleman (ouch).
The song "Fifteen" is actually about an occasion during Taylor Swift's freshman year in high school in which she was "tamed" with the Rowdy Giraffe maneuver after a boy said he loved her and that it wouldn't hurt.