Once on a flight LAX-TPE, about 2 minutes after we took off on this 15 hour flight is when I noticed the severity of the problem with a passenger seated two rows back. I am sure those seated immediately next to him must have noticed sooner but apparently no one said anything and once you leave the ground LAX-TPE, unless someone is in danger of dying, you are pretty much committed to being in the air for the next 15 hours no matter what. It was BAD. Really bad. The flight was full too. I just resigned myself to the reality and hopelessness of the situation. Shortly after the FA's got out of their jump seats and started moving about, apparently they became aware of the problem too and before you knew it a FA walked quickly down the aisle and discreetly let loose a spray of some industrial strength air freshener just as she passed him. Hardly a perfect solution but the stuff was remarkably effective at partially masking some of the smell. The flight attendants were very discrete about it but every 15 minutes almost on some kind of schedule for the whole rest of the 15 hour flight one or another of them would walk quickly down the aisle from the mid galley to the back galley with a quick spray of the air freshener right as they passed that passenger.