I get error java.util.UnknownFormatConversionException: Conversion = '!'

I have a string

String pat = "HelloWorld#$%!";

@FindBy(xpath = "//*[contains(text(), 'Best Choice')]")
WebElement button;

final String format = String.format("%s", pat);
final String format = String.format("%s=!", pat);
button.getText().contains(format); 

When I'm trying to compare my button with text fails with java.util.UnknownFormatConversionException: Conversion = '!'