Depends on their placements really. And also their spiritual maturity. Pisces is supposedly the oldest sign in the zodiac, being the last one, I feel like it depends on how evolved they are as well.
I have a lot of air in my birth chart so I tend to rationalise my criticism, where I'd only say something worth mentioning. I can contain myself pretty well and refrain from acting passive aggressive especially if I'm feeling quite emotional towards something.
I know a few Pisces that have water and fire placements, they tend to be more outwardly with their criticism and quite passionate about it too, even if it isn't logical.