Suppose that your spouse or family/friends decide that they can’t “surprise” you with something on your wedding anniversary or birthday because you would be expecting to get something on that special day, and so they try to catch you off-guard by staging the surprise party, or surprise gift, or other treat, a day or two *early *before the anniversary/birthday so that you will not be expecting it. Would you be pleased or irritated? (you do not get anything on your birthday or anniversary itself)
Assuming I’d still get at least a “well wish” on my birthday (the day wouldn’t be completely ignored, no problem.
Someone making an effort to remember me is always appreciated. While I don’t care for surprise parties per se, a surprise gift or card, or a lunch or dinner treat would be very sweet.
I have a several adult family members in town, and one of them for a while only had partial custody of his kid - due to scheduling conflicts there were a few years when we never celebrated a birthday on the correct day. It got to the point where one time it randomly happened that the birthday could actually be celebrated on the correct day, and we not-too-seriously considered celebrating it on some other day for tradition’s sake.
I think I could handle it being celebrated early.
I’m less certain how I’d react to it being sprung on me as a surprise - that’s literally never happened to me, because my dad is a scheduling freak and reacts very poorly to surprises. Well, that and there’s little chance everybody would be available.
What sort of psychopath would be ANGERED by friends doing something nice for them? And why would you ever do so again?
Well, depending on how they surprised me I could see it. I haven’t experienced a surprise party - do they do it like on TV, as a home invasion involving breaking and entering when they try to give you a heart attack?
For clarification:
Maybe “anger” isn’t the right word (far too strong), but since I specified in the OP that you get this surprise party/gift/whatever on the days ahead of your birthday, *rather than *on the birthday itself (your birthday is going to be treated like any other ordinary day,) would you be peeved at this, or take it happily?
It might change the words of my answer, but not the meaning. You’re not entitled to birthday celebrations at all (especially people over, say, 15 years old), and your friends/family did something nice for you. Being angered, peeved, irritated, or merely irascible about it seems bizarre to me. (Assuming no heart attacks, here).
Not keen on birthdays at the best of times, so no, wouldn’t be very happy.
I enjoy a quiet, chill day on my birthday with just my husband and daughter. It very often doesn’t happen because my birthday is December 26th, so there’s usually lots of holiday stuff going on. We also decided years ago when our daughter was young that Christmas Day was our day at home. Years later, and my MIL still has trouble wrapping her head around that. Anyway, she’s getting older, aren’t we all, so the past few years we’ve either had her here or we spend a few hours at her house on my birthday. It’s not what I’d choose, but we get Christmas and I love her dearly. It’s one of those things, it makes her happy, so a few hours isn’t going to kill me.
Those people would be working hard to demonstrate how little they know about me, which makes you wonder who the party is for. I would try to smile through the absurdity.
If you’ve told friends not to do something and they do it anyway.
I’m not a fan of surprises that are focused on me - I’m not that fond of the spotlight, and frankly, my birthday has never been a big deal to me. Twice in my life, I’ve had surprise parties - one in high school, and one that my husband pulled together. They were both nice and I do appreciate the effort made on my behalf. I also hope no one ever does it again.
In fact, a few years back, I deliberately avoided a situation where I was pretty sure my sister was planning something. We were on a family cruise that happened to include my birthday. I told my husband I wanted to dine in one of the ship’s specialty restaurants that evening because chances are, my sister was going to have the wait staff come over and sing to me and I absolutely didn’t want that.
Send me an e-card and I’ll be happy. Just don’t make a fuss over something that merely *happened *to me! Sheesh, it’s not like a personal achievement or anything! 
Nope, doesn’t bother me. My birthday frequently falls a few days after MLK day, so that long weekend has frequently been used for the celebration.
Late January in Chicago frequently has the worst weather of the year so I’m happy with anything
Sort of happened to me last weekend. My aunt’s birthday is in January. I called her the week before to arrange to take her out, but she had an injury and couldn’t make it, so we agreed to do something once she was healed. In March, she called me, but at that point I was injured and couldn’t make it, so we agreed to postpone again. Finally I called her about 10 days ago, and we agreed to go out to lunch. In my mind, this was her very belated birthday celebration. But after we ate a nice lunch, the waiter came over with a dish of ice cream that had a lighted candle in it, and she wished me a happy birthday. I was a little confused, because this was supposed to be her birthday celebration, and my birthday is in August. But I went with it. The important thing was spending time with her, and it didn’t really matter who was celebrating what. BTW, we would have been celebrating her 82nd birthday.
If I had told someone I didn’t want a surprise party and they did a surprise party (early or not), I would be angered.
If my schedule is jam-packed and everyone knows it, but they went on and (unknowingly) scheduled a party for a time that is inconvenient for me (like right before I have to catch a flight for an important trip), I would be a little ticked off.
These are the only situations that I can think of where I’d feel anything close to anger. Otherwise I’d be happy or neutral.
The OP says nothing of the sort, though.
Being a fairly normal human being, I’d be pleased.
It’d be a huge shock/surprise, and depending on my day, I might be feeling somewhat anti-social or tired, but once I saw all my friends and family gathered… let’s have a party! My birthday is as good as any other excuse to get together, but I’d feel honored and would have no trouble celebrating with my loved ones.
As someone who had a surprise birthday party very recently, I can tell you I was THRILLED. Some of the people who organized it were quite clever: I knew I was going to brunch and they made sure I was dressed cute 
so I would be happy with the video of the event.
It was fantastic!!!
Celebrating my birthday/anniversary early - no problem.
The manner in which I’m surprised, may or may not be a problem. TV Sitcom style surprise party where I am coming from somewhere, completely unaware that lots of people are at my house, would probably freak me out. I like my routine. If I’m coming home from work or whatever, I’m looking for relaxing and quiet, not a party.
On the other hand, if my friend said to come over Friday evening for dinner and I got there and many of my friends were there for a party, I would be quite pleased.
I wouldn’t want people coming to my house when I wasn’t expecting anyone because I wouldn’t want to be embarrassed if I didn’t feel company-presentable but other than that I wouldn’t care.