This one was easy to miss (and I did miss it the first few times) because it occurs during a time of tension when Michael, Sollozzo, and McCluskey are being driven to Louis' Restaurant.

While they're in the car, McCluskey tells Michael, "Sorry about your face..." blah, blah... "I must be getting too old for my job..." blah, blah... Then he puts his hand on Michael's shoulder and says, "Aw, he's a good kid." Michael looks down at McCluskey's hand patting his shoulder as if the guy has leprosy. You can almost hear Michael thinking, "Get your stinking paw off my good coat."

Good one, Michael.