Need

Is "I need" the worst way to ask someone to do something?

I thought so.. as in "I need you to fill in this template". Just saying "fill in this template" may look worse at first but I don't think it is.

Now I think just "need" is worse. Yep, this is what really happened to me one day. An email from my manager, "Need this filled in by COB today", with a spreadsheet attached.
Not even "need you to fill this in by COB today". Let alone a please thrown in to at least make it look like a polite request.
On top of that, the template was far from self explanatory and there was no attempt to provide the context or ultimate objective of the exercise.

Not surprisingly, what he received wasn't what he wanted, or needed.
I prefer to use "would you please...?" followed by the context or as I've heard it called "commanders intent". That way there is a good chance that anything not clear in the instruction will be cleared up when they read the objective. It also helps them feel part of the bigger picture and gives them an opportunity to add their thoughts. Funny thing is that when he sent the email I was sitting about 10 feet from him in talking distance. When I read it about 10 minutes later, he was gone so I couldn't ask for some more details. Not just gone to a meeting or something, packed up and gone from the office.
Now if I was a smartarse, I could have just ignored it. He wasn't asking me to do anything, just making a statement on something that he needed. I could have replied, "OK, good luck". But I'm not always a smartarse, so I polished my crystal ball and did what I thought was required.
I can't help thinking the next step didn't work out for him and wondering if he threw me under the bus. As in: Oh, I'm sorry I didn't get that done because I was let down by Harry. Was that his plan all along? Not enough time to explain it to me, or he didn't know what had to be done, so he set himself up with a nice little excuse. Obviously I won't know but I can learn from the experience and make myself a better person out of it.

There are two reasons I don't like "need" at work. A need is something you almost can't live without, or at least something very important. As in "I need food", or "I need help with my homework".  It's also something that requires the other person to care about enough to want to help. In a work situation, if a respected collegue was in a position where he could lose his job and needed help, I'd probably ask how I could help and do the best I could to help them. On the other hand, some jerk who needs help to protect his false image is going to get the bare minimum that their role power deserves.