Explanation: The ultraconservative Senator Cato the Younger, an enemy of Julius Caesar (of conqueror and dictator fame, though at this time he was neither, just a reformist politician of moderate importance and infinite ambition), once saw Caesar receive a note during a tense time in the Senate, when the Catiline Conspiracy was ongoing. Caesar had a tendency to read in silence (ie in his head) which was unusual in Roman society, being seen as furtive and secretive. Cato, seeing a chance to attack his longtime foe, accused Caesar of being with the conspirators, as evidenced by the note he received!
Wordlessly, Caesar gave him the note. Triumphantly, Cato began to read the note to the Senate, until he realized it was a love letter from his sister to Caesar. Humiliated and frustrated in his aim, Cato threw the note back at Caesar and called Caesar a drunk - especially funny since even Cato's defenders noted he was a heavy drinker, and even Caesar's enemies admitted he was not much for boozing.