Stands for No Upgrade for U Bitch! Used by airline staff, but spreading to the queue, when some monied princess, having bought the cheapest ticket known to man at the back of coach, demands an upgrade for her and her travelling circus of friends and relatives. They think just because Princess Margaret got away with it regularly to Mustique, it should be automatic for her too. It isn't. But she never gives up.
"I swear, the next NUFUB I get checking in, I'm gonna rip her throat out."
I get so embarrassed when mom tries her NUFUB tactics at check-in. It never works.