When a male or female lays done on their back and their partner crouches with their ass in front of the other persons mouth. The person laying down licks their partners asshole untill they eventually start shitting and it gets all over the other persons body. Thus the "Chocolate" starts "Rushing" forming a "Mountain" on the perosn laying down.
dude she totally gave me a chocolate mountain rush last night bro, shit got EVERYWHERE!
Mary wanted to try taking it in the ass on the old kitchen table but it was shaking up so much it ended up a big ole' Rocky Mountain Chocolate Factory in there.
The act of vaginal penetration via doggy style during which the female excretes fecal matter for lubrication upon the male's penis.
Dave: So what did you and Jill do last night?
Aaron: She gave me a little Rocky Mountain Chocolate Factory.
Dave: You mean where she shits on your dick to lube it up real nice?
Aaron: That's the one!
Dave: NICE!!