Batman gives him the definition, but Robin doesn't understand it. So Batman comes up with some hypothetical situation and uses it for the explanation. Robin still doesn't get it. Batman comes up with another example with lots of details. He's dancing around, singing, drawing charts, etc.. but there's still no sign of any idea in Robin's eyes. Finally Batman loses his temper and tells Robin to drop his pants. As Robin does so, Batman shoves his dick up Robin's ass and says, "You see, I've got dick up the ass, and you've got dick up the ass. But there's nuance"