This is going around Facebook, and it irks me to no end because I've had Crustys give me this rant while holding up a line just to get their point across. So here's my response, and it's still nicer than what I wanted to say at the time:
A holiday is a day fixed by law or custom on which ordinary business is suspended in commemoration of some event or in honor of some person. So, yes, actually, Christmas is a holiday, as is Thanksgiving and Easter. We say "happy holidays" in retail because we don't know which holiday you celebrate and there are several celebrations that take place in the same month. How am I supposed to know whether you are Jewish or Christian? Should I assume that because you're black that you celebrate Kwanzaa, while completely disregarding the fact that you may, in fact have been raised Catholic?
You wouldn't appreciate it if I asked you your religion first, and a lot of people get angry at us if we are mistaken enough to assume that you celebrate Christmas instead of some other holiday. You claim to 'respect' other holidays, yet you are offended because we are trying to open our minds to all holidays by wishing you well, no matter the holiday you celebrate. Please stop sneering at us for that, as we cannot win no matter which holiday we bless you on.
And while yes, corporations need to include more celebrations in their decorating and celebrating another year of corporate greed, retail workers say "happy holidays" because it sounds nicer than "happy what-ever-the-fuck-you-celebrate."