The idea of a friendly crocodile comes from a children's rhyme or story I heard when I was younger. I can't really remember it but I'm pretty sure the moral ended with the friendly crocodile eating a few children that got swayed by its charms. For this reason I think it was written by Roald Dahl. Who had several kids, and even some adults, meet their end down the gullets of giants, rhinos and other menacing creatures.
For this reason I wanted my crocodile to appear very debonair and affable and a contestant for least likely to swallow and digest anyone. So when it ever did come to devouring it would come as a complete surprise.