How much damage would it be possible to do in the 3 - 4 minutes it will take me to go back to Facebook, go to my account settings, look at my app settings, find the app in the huge list, and then start removing permissions I don't want to grant it?
After that I have to go through the effort to find the post content in my timeline, one by one delete the items and hope that my friends have not yet seen the content (and it being posted to the ticker makes that unlikely...)