Once on a transatlantic (a rare vacation one) I was seated across the aisle from a woman who kept dragging out this really nasty perfume/whatever and putting it on/waving it under her nose. Couldn't stand it, so I directed my vent at her. She then proceeded to get very cold and huddle under a blanket (while still doing the perfume thing). My mother (I was 25 at the time) came back to her seat and made me turn the vent off as it was rude to make the woman suffer. As soon as I did though, she immediately told me to turn the vent back on her. Not the nicest thing I ever did, but it was better than spending 10 hours with that smell.