Why did the hutus in rwanda hold a deep hatred for the tutsis?

This hatred goes at least back to the colonial times: the Tutsis were favoured by the colonial power (the Belgians) and there was the concept of rich Hutus being allowed to become "honorary Tutsi".
The Tutsi were also a minority: so they were a powerful minority and the Hutu were a less-powerful majority. This influenced the dislike the Hutu had for  Tutsis.