Top Definition
When you fuck someone really hard.
You fuck someone so hard it's like a train getting derailed off the tracks.
"Greg derailed that bitch"
"I thought he had mono!"

"I'd derail her."
by Turbulence n' Jeff November 12, 2007
one who gets plowed like a piece of land; one who gets laid the fuck out, one who gets bombed by sharif
Holy shit dunne just got derailed and broke his wrist.

WOW, Pauly Tess just got derailed.

HOTDIGGITYDOG, Stup just got lined up and defuckinrailed.

Wilferd Brimley here, If you or someone you know has dyabeetus and got derailed call Liberty Medical now.

by Wilferd April 22, 2010
The act of pounding the living shit out of a biddie's/whobag's gloryhole. Possible after effects include, concussions, vomiting, dizziness, loss of sight, vaginal reconstruction, scoliosis, hernias, coma, and even death.
Franky D-Wet: Shit man, da fuck happened last night? And why is my dick so fucking sore?
Meech: Bro, you were reDICKulous, you De-Railed the fucking life out of some who-bag. You should probably stay low for a while, they found her dead this morning with serious spinal injuries.
by Franky D-Wet February 26, 2011
1. During the act of doggy-style vaginal intercourse, the male, while recovering from a thrust, pulls out too far and his penis "accidentally" inserts itself into the girls anus.

2. An arctic map in the video game "Call Of Duty: Modern Warfare 2."

"The other night my girl moaned some other guys name, so I derailed her. See if she does that again..."


"Last night I was having some fun, then got derailed"
"You pulled out too far and got mud on your junk?"
"Worse. I got that shitty snow map."
by FunkyPunkyJunky March 20, 2010
A women losing her virginity in a very rough, hard manor.
Guy 1:Dude, I totally just derailed this one chick!
Guy 2: Me too!
by Wendy (bob's girlfriend) October 11, 2008
to fuck the shit out of somebody, then never talk to them again despite seeing them around a lot. Usualy occurs between upper and lower classmen in high school and college.
bro 1: jon derailed that chick at that party
bro 2: I know, shed in two of his classes to
Bro 1: awesome
by jon Appleseed July 29, 2008
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