if you want to invite me to party, ASK ME first.

It doesn't. If someone harasses you it's way beyond a "ninja" invite...

110% agree with the OP.
Yes, I probably am what is considered "Old School". So be it.

To me it's like shoving your money at the busdriver and then expecting .. what?
For him to be a mindreader and know where you wish to go to? For him to ask "Where to?".
Perhaps you could say "Goodmorning, this destination please." as you give him the money?
Common decency just isn't common anymore, I guess. Yes, I'm aware different people are accustomed to different ways. I am very aware : )

Having said that, I DO realise that most blind invites aren't intended badly, even though they may come across as rude to some of us. I, like many other posters here, just do not like them if I've no idea what you're inviting me for.
And these are the keywords, which many of those disagreeing with the OP are conveniently ignoring: "IF I've no idea what you're inviting me for." That is when a blind invite becomes annoying.

@Sweeper: Obviously if we're asking in /General for an FP and get sent an invite, that is not perceived as rude. We know what the invite is about, we were asking for it.
Keywords reminder: "IF I've no idea what you're inviting me for."

@Several others: Yes, if we're staring at the same mob spawn for the same Elite, we understand why both of us are here. We'll understand what the invite is for.
Keywords reminder: "IF I've no idea what you're inviting me for."

@Yet several others: If I happen to be in an area with you, we do not know which part of which quest the other is on. Maybe the other is just starting, or just done. Maybe I'm just standing there cos my little kid just woke up, or the phone rang. Maybe I'm waiting for a friend to arrive to do the quest with.
Keywords reminder: "IF I've no idea what you're inviting me for."

I'm not your next NPC.
I'm a human being behind a keyboard, just like you. Communicate. Talk to me. What is it you would like to group for? Maybe we can help eachother, maybe not.
If you plan to treat me as your next NPC, then I agree with those that said above they might as well pull out their companion and run with that instead.

---

I'll share my little gem from a few days ago:

I just arrived with my new alt at the Fleet and am standing at my trainer, checking the Advanced Skill Trees, trying to decide.
A blind group invite appears on my screen from.. let's call him SilentJoe. I continue to read my Talents, leaving it unanswered.
From the corner of my eye I see my General Chatwindow:
SilentJoe invites you to a group
SilentJoe invites you to a group
SilentJoe invites you to a group
Being in a fairly good mood, I do not roll up my sleeves to give SilentJoe a piece of my mind, but send him a /w asking him if he cares to explain or is just planning to keep spamming blind invites my way.
He replies "Oh, sorry." (indeed no bad intentions, just.. thoughtlessness?)
"Hey, would you mind group with me for guild?"
I'm still not entirely sure what he's after, but as said my mood is good so I accept and end up in group with 3 other pple. I check to make sure he is asking help to start up a guild.
Yes, this is the case.
Then the fact that I'm already in a guild, will probably be a problem.
"Oh sorry, ok. Thnx"
I sighed to myself and shook my head. I wished them luck, left the group and returned to my Skill Trees.

These days, if an invite suits my needs I'll take it.

Admittedly, I WAS very annoyed when I first posted, but it's amazing how seeing a bunch of viewpoints and really thinking about them can bring you back in perspective

It took a while, reading the various posts after yours, for me to understand what the real issue was here. As I've tried to say, I don't think most people do the "ninja invite" to be rude. I say, but I cannot prove either way, that most people do it because they think it's more polite - especially noobs. Yes, re-asking 10x and interrupting a fight and all that is bad and douchy, no disagreement. But if everyone is standing around re-spawning for a heroic, it seems like it should be okay, no?

But in any event, I think my main issue with your post is that it assumes people are being rude or lacking in manners, when many are just noobs who are still learning the proper etiquette. Heck, for me I deliberately did NOT whisper because I assumed that would be more intrusive and/or creepy - pure noobishness, not rudeness. I think the point about the popup window with invites captures a lot of the problem too.

Agreed. That's the thing. Harassment by ninja-invite is a problem because it's harassment. The means of harassment is not material IMO. That example doesn't really have anything to do with the matter of whether or not it is rude to invite without sending a tell first because a single invite is not harassment.

Ok let's stop with the ninja invite stuff...it's simply an invite. There is no button that says ninja...and 999 out of 1000 people are just trying to be social to accomplish a common goal..

Does it bother you ?