In Act Three, scene two, of Shakespeare's The Taming of the Shrew, I believe that Petruchio arrives to his wedding in old clothes for several reasons, all of which center around Kate and her attitude.
Kate is used to getting her own way. She has a well-known reputation of being a brat. It is in this way that she exerts her control over not just the family in general, but also over her sister who cannot marry until Kate is married. Who, then, would be brave enough to want to marry Kate? She can remain single as long as she wishes. Kate believes that she can control any man. Petruchio's word play with Kate has probably impressed her, but she is not ready to give up the power she has for a man. She seems comfortable with her situation in that she also doesn't seem to mind that she is called a "shrew." It is, after all, on her terms that she lives her life.
By coming to the wedding in awful clothes, Petruchio is first doing something that Kate would not expect—perhaps sending her a "wake-up call." She does have her pride. We see this when she begins to cry, believing that Petruchio has left her at the alter at the beginning of the scene. She will expect him to come nicely dressed for her sake...because it's what she wants.
Petruchio is showing Kate that he will not bow to anyone's expectations, and he explains to the men who greet him when he arrives that Kate is not marrying his clothes, but the man in the clothes.
To me she's married, not unto my clothes... (112)
Finally, I believe that Petruchio is sending Kate the message that he is his own man. He is not afraid of her, neither will he be intimidated by her as so many men before him have been. He is letting Kate know that he is the boss, without saying a word.