I'm voting JAN BRADY! I mean I wasn't even ten when I first saw that episode but even back then I thought her 'KA-CHOO-ing during the Tiger giveaway episode of the same name was totally fake and couldn't understand why her folks wouldn't have just sent her to school and told her knock it off!:lol:

She IS a bad faker. I don't remember too many sneezes from the others, except that Cindy came down with the sniffles at the most inopportune times!

it sounded more like she was getting stabbed rather than sneezing

Jan's the only one I really can recall sneezing except for Cindy in "Coming out Party"

Peter sneezed as Sneezy in the Snow White play, but that wouldn't count since they weren't supposed to look/sound real. I can't think of any other sneezes either.