When you are entering your Shih Tzu into a dog show you should carefully choose what to wear. Certainly, you will not be judged for your appearance; however there are 2 elements to keep in mind.
First, there are rules and guidelines on proper dress. Each club and event will be able to offer you a document with details.
Secondly, you will be in front of many people as well, as you walk and show your dog. You will also be in photographs, should your dog win a ribbon.
Therefore, you will want to look your best. Each show has their own dress code; however most will ask for business casual.