It’s a very long story…

He knew many jokes about Vovochka, but didn't think there were jokes about him too, and so, the students and Vovochka met James, and he started telling jokes about Vovochka... But these students were no fools; they had long anticipated this and stuffed their own and Vovochka's ears with earwax! And the attack failed, so the students strained all their brain cells and started making up jokes about James on the spot, and, seeing that their brain cells weren't enough, they called Poirot too...