covered here many times.

For the better part of the last decade, when in my 20s, and as a dilligent member of FlyerTalk, I have learned how to use the system of miles and points to my advantage, and about 25% of my flights during my 20s (all leisure) were in premium cabins..

During that time I have met many passangers (funny enough, never really the crew) that questioned my "belongingness".

After the famous $1400 BIZ to AKL deal on United, I was waiting in line (after backpacking for a month around NZ/OZ) at SYD checkin, and this 50+ yr old dude with a big 1K tag on his hand luggage, told me:
This is the business class line, you have to pay over $10 thousand for these tickets... when I told him how much I paid and proved it with my receipt, if looks could kill..