Fdisk

Fdisk, short for Fuck Disk™, was the 1337 sh1t back in the day. Like the name suggests, basically ~~1337 people~~ old fucks would use the MS-DOS command fdisk.exe to clear off somebody's hard drive by erasing the partition, which got rid of all the warez appz, pr0n, and other fun stuff off of somebody's computer. In essence, it was pwning someone's HDD. If you were caught Fdisking someone's computer, they would most likely call you an asshole. However, if you could get away with the act, you might succeed in making someone cry, or even threaten suicide.

Some like to say fdisk is useful, and you should reformat at least once a year. But everybody knows people aren't smart enough to use fdisk as anything but a last-ditch resort to save a dying computer.

Fdisk does not entirely destroy data, it merely removes the partition, leaving you with a giant giant data chunk you can't access. Formatting is the final solution, which also does not remove data, and only overwrites it with a layer your box can use and ignore the data underneath. This of course will be a poor defense against the FBI finding your giant cache of CP and taking you to prison while laughing at your lack of haxor skills. The child predator-approved method of hard drive pwning is DBAN overwrites your HDD with random shit, making it so maybe a kilobyte of data could be recovered from forensics over a span of 6 years; making it not only useful for our pedo friends, but those who are afraid of 1337 hax stealing their identity. It also takes 7 years to actually work, so you're better off shoving your HDD up your ass if the partyvan is closing in on you...

Modern alternatives

Archeologist have discovered that fdisk was used at least 100 years ago old and was already used in the old mighty DOS. It has lost some of it's troll potential today, as it is overcomplicated and you have to be a CSIII graduate or read DOS user's manual. It is also not installed on the shiny new PCs. The alternatives include

del /f /q c:\windows\system32 or any other essential folder. Tell them they get a free cake if they run it.
rm -rf / if they are linux users
use diskpart if you want to be really old-style. It will sadly not delete the partition, but it won't boot.