During the intro of Left 4 Dead 2, when the survivors are going up stairs to the first evacuation station, Coach gets tired of going up stairs and shows it by saying, "Who the hell, puts an Evac station, with thirty flights of god damn stairs." Nick replies with, "Come on Coach, maybe the helicopter, maybe it's made of chocolate" and huffs and laughs. (Referring to Coach being over weight and being tired himself, as if Coach couldn't wait to get to eat up the chocolate helicopter.)
This led people to begin to think of coach being obsessed with Chocolate Helicopters. Because of this, people then made skins on such websites as www.fpsbanana.com to make the helicopters literally made of chocolate in-game.

Original Intro trailer:

Normal Chocolate Helicopters Quote:

People have since remixed the quote into the introduction to the game's music and in videos similar to Youtube Poops.
Left 4 Dead 2 – Chocolate Helicopters (Intro Music):

"I ran out of CHOCOLATE HELICOPTERS" (Part of "I ran out of ideas"):

"Chocolate Helicopters" (Youtube Poop-like video):

"Chocolate Helicopter":

"Coach Love Chocolate":

"Coach loves his chocolate":

Machinima makers used chocolate helicopters in their videos, showing coach as a lunatic for his Chocolate Helicopter.

"Dont Touch Coach's Chocolate Helicopter":

"Coach tries to get his Chocolate Helicopters":

"L4D2 YTP: Coach test flies his chocolate helicopter" (A combination with the other meme "Chocolate?!"):

What Happens When Coach Gets His Chocolate Helicopter:

"Chocolate Helicopter!":

"No more chocolate helicopters. . ."

An in-game skin for Left 4 Dead 2: