Where I work, I will be seeing 1000’s of people over the holidays. I plan on saying “Happy Holidays” to people. Last year there were some who took offense and would angrily and loudly proclaim “MERRY CHRISTMAS!!!” to my very innocuous “Happy Holidays!”.
I never know how to respond to someone angrily shouting Merry Christmas at me. It doesn’t sound very merry.
Just say, “and a happy holidays to you too.”
Say ‘happy ramadan’.
Ignore them. You’ve already wished them a happy holiday and they’re trying to pick a fight.
“Okay, Merry Christmas and I hope your New Year’s Day sucks.”
It isn’t merry, and it isn’t meant to be. It’s an infantile passive-aggressive way of trying to force you to validate their way of thinking. Don’t fall for it.
My standard greeting around this time of year is to say, “Enjoy your holidays!” Regardless of how someone responds, I simply smile and go on my way. If it’s one of the jerk types you’re describing, my smile tends more toward the indulgent-toward-small-children-throwing-a-tantrum variety.
I’d be tempted to go with “Hail Satan.”
I just tell people to have a good day.
Do what you want, but consider that what you say could be applied to those who say Happy Holidays as well. It all depends on the intent behind of what they say, and they are many people who say happy holidays with the infantile passive-aggressive intent of trying to force them to validate their way of thinking.
Invalidating a tradition (or a traditional saying) is done for a reason.
I have GOT to remember this when I talk to my sister this December.
If they sound angry when declaring a “Merry Christmas”, how about responding with “good luck”?
Happy Ramadan!
I’ve actually said this, preceded with “Why thank you…” and ending with turning and walking away.
I’ve always wanted to say, “WHAT’S MERRY ABOUT IT!”. 
Same with “WHAT’S GOOD ABOUT THE MORNING!”
BTW, I usually pretend to be a Grinch/Scrooge around the holidays, but every knows I’m just playing around.
Edit: Makes it hard when I’m really upset at something though, since I’m generally known to be always smiling and joking around.
Actually, this year I’m getting a LOT more Happy Holidays than in prior years.
“Go fuck yourself”
“I’m not you”
“I don’t care”
“That’s great”
Etc…
Just checking: these people weren’t all four years old, were they?
One day I’m going to quit via epic meltdown and that is what I’ll say 
No, these are (mostly) middle class, white seniors.
Ignore them. I guarantee everyone who overheard knows they are being jerkish.
You could look deep in their eyes and calmly, slowly, softly, deliberately say “I hate you” as if you really mean it. Turns out this is really surprisingly creepy and disturbing.