It seems that krokodili means when two Esperantists speak with each other in a language other than Esperanto, what is the origin of this use?
Wiktionary offers several possibilities:
"From crocodile tears. A crocodile sheds tears while eating its prey. The krokodilanto bemoans the fate of Esperanto while not bothering to speak it."
There are some rather persistent stories about an Esperanto instructor who had a crocodile hand puppet. Supposedly he used it when he would occasionally answer a question from a beginner in their native language rather than in Esperanto. Thus, only the krokodilo spoke in any language other than Esperanto.