I was in economy next to some one who was 'size challenged'. Less than ecstatic at the prospect of several hours with him spilling over into my seat, but the flight was pretty full so decided (without much hope) to keep quiet and look for an empty seat after take-off. He started a campaign for an upgrade on the basis there was insufficient room for him. After a fair old rant the CSD came and agreed it was unreasonable to expect him to sit next to another passenger - and asked me (almost apologetically) if I had any objection to an upgrade. Beautifully done. The guy was furious - he had obviously got away with it several times before. Made my day.