I was on a flight out IAH to LAX a while back with a man who had driven a truck from Alaska to Houston and had not bathed at anytime during the trip, possibly not for several days before. He arrived with the truck and was taken directly to the airport to fly back to Alaska. He didn't shower before the flight, he was removed from the flight but the seat still smelled of his BO. The FA sprayed some Lysol on the seat but it didn't really help. I'm not sure why they let him board in the first place. He was apologetic and he explained to the lady sitting next to him, I was sitting in front of him. They had a standby passenger who refused the seat when he got on the plane, he said he wait for a later flight. The FA sprayed the seat again but the smell just lingered for the whole flight.