Opposed to fucking somebody up, this will almost always end the beings life. To fuck somebody or somthing down, while walking behind the person or object you must vigorously leap into the air over your enemy, at this time you will be hovering over them. Once you are succesfully hovering over the human you must pelvic thrust their cranium into the cavities of their chest.
Dude, i just fucked that guy down. I think hes dead. I love to fuck down!