In Act I, Scene I, the commoners are celebrating Caesar’s return to Rome. However, not all Romans are happy about this. Marullus and Flavius are Pompey’s men (Caesar’s conquered rival), and they want the celebrating Romans off the street. In fact, Marullus is insulting about it, saying to the people:
You blocks, you stones, you worse than senseless things!
O you hard hearts, you cruel men of Rome,
Knew you not Pompey?
A foil is a character who contrasts with another character in order to bring out important qualities in that character. Marullus and Flavius are very stern and serious, but the Second Commoner (a cobbler), no doubt due to being at least slightly inebriated, is full of mirth. He annoys Marullus and Flavius with his punning chatter. When they ask the Second Commoner why is leading men about the streets, he says:
Truly, sir, to wear out their shoes, to get myself
into more work. But, indeed, sir, we make holiday,
to see Caesar and to rejoice in his triumph.
The joke is that he is leading them around to wear out their shoes so that they will have to come to him to have their shoes repaired. Flavius and Marullus don’t think it’s funny.