Not really. You can always wear birthday squad shirts more than once. Surely, nobody would object if you wear them at home while you do some gardening or some grilling, or even while you work out. However, if your shirt doesn't have the word "birthday," doesn't have the birthday celebrant's name and age, doesn't have your name or a description of your personality, and is overall safe and generic, then you can definitely wear your shirt again when you go out.