The length of time it takes for a man to move the tip of his penis one mile in the reference frame of the vagina while having intercourse.
The following formula can be used for a simple calculation: (63,360 inches / 2*(penile length)) * (Average thrust time), where penile length is in inches. The units of average thrust time will determine the units of the fuckmile.
Hey...remember that night we dressed up as 32nd century wizards, snuck out to the club, ordered a vegan chili dog, ran three miles, and then bought two six packs of dr. pepper? And we did it all with the fuck mobile!