I've done it a few times for different airlines, QR included, and everyone so far has been very appreciative of it. Given I have friends who work for EK, QR, BA, LH, FR, EZY and EY (as well as others who previously worked for other airlines) and hearing about their horror stories, I can't help but think that a small gesture like some chocolates makes their job that little bit more satisfying, giving them peace of mind that not every passenger is a complete A-hole.