Totally stole this entire thing, but since I stole it from two different sources it works out to being independently verified twice! So, yeah. So there!

 Sitting together on a train, travelling through the
Canadian Rockies,  were an American guy, a Canadian guy, a little old Greek lady,  and a young blond German girl with large breasts.
 
The Train goes into a dark tunnel and a few seconds later there is the sound of a loud slap. When the train emerges from the tunnel, the American has a bright red hand print on his cheek.  No one speaks.
 
The old Greek lady thinks: The American guy must have groped the blonde in the dark and she slapped his cheek. The German girl thinks: That American guy must have tried to grope me in the dark, but missed and fondled the old lady and she slapped his cheek. 

The American thinks: The Canadian guy must have groped the blonde in the dark. She tried to slap him but missed and got me instead.
 
The Canadian thinks: I can't wait for another tunnel, just so I can smack the American again.