Where is the theme of honor shown in Act 1 of Julius Caesar?

Marullus and Flavius question the honor of the townspeople for celebrating Caesar’s victory over Pompey, and Cassius discusses Caesar’s honor with Brutus.

Marullus and Flavius are upset because the townspeople have gathered for a holiday, adorning Caesar’s statues.  They remind them that not too long ago they were celebrating and admiring Pompey.  In their minds, it is dishonorable to rejoice at Caesar’s victory over Pompey, a consul of Rome.

And do you now put on...

Marullus and Flavius question the honor of the townspeople for celebrating Caesar’s victory over Pompey, and Cassius discusses Caesar’s honor with Brutus.

Marullus and Flavius are upset because the townspeople have gathered for a holiday, adorning Caesar’s statues.  They remind them that not too long ago they were celebrating and admiring Pompey.  In their minds, it is dishonorable to rejoice at Caesar’s victory over Pompey, a consul of Rome.

And do you now put on your best attire?
And do you now cull out a holiday?
And do you now strew flowers in his way
That comes in triumph over Pompey's blood? Be gone! (Act 1, Scene 1)

They feel that the citizens are betraying Pompey by following Caesar.  Caesar crossed the Rubicon and marched on Rome when Pompey was in charge.  He then defeated Pompey and many other Romans, some of them senators and high-placed businessmen.  This is one of the reasons that everyone keeps calling Caesar arrogant.  They can’t believe he would break the law to take power and then make war on other Romans.

When Cassius and Brutus are discussing Caesar’s arrogance, Cassius tells Brutus that one of Caesar’s greatest sins is that he puts himself above others.

Why, man, he doth bestride the narrow world
Like a Colossus, and we petty men
Walk under his huge legs and peep about
To find ourselves dishonourable graves.
Men at some time are masters of their fates:
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings. (Act 1, Scene 2)

This means that if they choose to serve under Caesar, it is their own fault.  They can be slaves if they choose to be slaves.  It is up to them to decide their own fates.  To Cassius, the dishonorable decision is to just sit back and let Caesar take over Rome.  Like Marullus and Flavius, he believes that Caesar has overstepped and has to be stopped, for the good of Rome.