Page "Caligula" Paragraph 15

After he became Emperor, Caligula claimed to have planned to kill Tiberius with a dagger in order to avenge his mother and brother: however, having brought the weapon into Tiberius's bedroom he did not kill the Emperor but instead threw the dagger down on the floor.

Supposedly Tiberius knew of this but never dared to do anything about it.

Suetonius claims that Caligula was already cruel and vicious: he writes that, when Tiberius brought Caligula to Capri, his purpose was to allow Caligula to live in order that he "... prove the ruin of himself and of all men, and that he was rearing a viper for the Roman People and a Phaëton for the world.