Eureka, new way to fool

Newton was relaxing under a tree when an apple fell and he discovered the law of gravitation. “Eureka” Archimedes was blissfully taking a bath when he realised the buoyancy principle.
My friend was continuing his lecture, when I interrupted: “Why this sermon?”
“Well, whatever you do, just relax and enjoy.”
By then, we had reached the canteen. He ordered sandwich and mint coffee.
“I am telling you all this so that you learn to take things easy,” he continued.
“I am ok. I do not get worked up over silly things,” I boasted.
He gave more instances of how to handle stressful situations.
“Are you sure you are a cool cat?” he asked.
I smelt a rat but like a fool blurted, “I presume so.”
“Well then, quickly pay the bill.”