When I was in school as a child, I probably had the loudest sneeze and always did that unintentionally, probably because I was too young to know I could physically stifle it.
I would scare the crap out of my classmates and teachers but I never had any teacher say anything to me about the loudness of it especially when I've sneezed in their classrooms close to 10 times. I've always felt bad for the numerous loud sneezes afterwards.
Oh, yes, I hate it when I'm about to sneeze, whether indoors or out, and my body's like "NOPE! Not now!"
That upsets me for some reason.