as many others have said, you dont know their business
maybe they have saved a portion of their earnings for a few years to afford holidays
maybe relatives have given them a present ie the hol as a pressie
maybe they have come into some money/won bet/won lotto
mayhe you should mind hour own business?
and hols in the sun have come down in price, so who knows, maybe they booked it 2 yrs ago, saved every penny for it
etc etc
i hate the way others compare themselves with those doing something nice and become suspicious or jealous. just be happy for them?