Probably the dumbest thing I've seen and can remember was a while ago in an old Marlboro commercial. I was looking for old commercials for a project and, as usual, I read the top comments.
There was this dude saying "I've been smoking since I'm 11, I'm still good and doing well." then a reply was something like "smoking hurts your lungs". Then the idiot came in saying "smoking makes your lungs stronger. You're breathing heavier air, therefore you're forcing your lungs to do excercise and you're making them stronger.", something between those lines.
Found it: