A condition sticks around until it's alleviated, so someone could possibly tap it more than once. Unless, of course, tapping it would get rid of it, which can happen. Consider: Alicia is Ostracized right now. Daniel tries to persuade her to help him out. Now, everyone knows that Daniel is the coolest, so he's like "Hey Alicia, why don't you tag along here?" The player wants to use Ostracized against her- obviously she'll jump at the chance to be seen with super cool Daniel, right? So sure, he gets to use it, but once everyone sees her with Daniel, well omigod wtf she's part of the cool kids now?! And Ostracized maybe goes away and no one else gets to use it again.
My personal instinct would be "no stacking Conditions" 'cause a +5 or whatever is crazy. But then again, maybe it makes sense sometimes? Like someone has been kicked so hard they'll do anything to stand up again. They don't stand a chance.