I've just about quit coffee.
At 1 point 3 or 4 years ago, I was having almost a pot a day (8 cups+). Got really obsessed with it; got a super fancy coffee machine that did everything right (temperature, water filter, etc...) - that's when I started having heart palpitations. Realized quickly enough it was the coffee causing that and got rid of that coffee machine, but stuck with the 4-8 cups a day.
It made me really irritable; hard to sleep - all the usual side effects.
I once tried cold turkey - no coffee - don't do that - it didn't work for me - headache's were amazing and irritability was higher then when I was on it and I quickly started drinking coffee again.
TBH, Cutting back to 2 cups a day was easy. I still have my first cup within an hour of waking up to make sure I don't start going through withdrawal.
I've now cut back to 1 cup a day for the most part - theres always coffee socially though - be it at a fancy dinner or a birthday party or etc... so it's never just 1 a day - period. Our society doesn't work like that. But 99% of the time, I'm down to 1 cup / day. I enjoy the taste of coffee (black, please) so I don't think I'll ever quit - but to much of anything is bad for you.
Now if I could just quit smoking, hahah.