A chocolate banana monkey is when you're getting it in the ass and you have to shit. A little bit comes out on your guys dick, creating the chocolate banana and he goes screaming like a monkey.
Coined from a popular pudding flavor, this is the sexual act when you slip out of hole #1 and accidentallypenetrate hole #2. To effectively acheive the "Chocolate Banana Surprise" both parties involved should be unexpecting this to happen, which will most likely lead to chocolate on your banana.
Dude, I was doggin' my wife last night and accidentally slipped it in her butt... that was the best Chocolate Banana Surprise ever! I bet her balloon-knot is sore today!