I was playing Sacred 2 the other day, and while I have most of the trophies in the game there is one I may never get. It requires you to talk to various characters in different cities in a particular order. One mistake and you have to start a new game. It's nearly impossible to get in a regular playthrough unless you look at trophy requirements before you start playing and are then very careful about whom you speak to.

What trophy/achievement have you found that seems to have a ridiculously high threshold for completion?

ETA: I distinctly remember this as a hidden trophy but can't find it now. I must have gotten my games mixed up?

Oh my, that sounds like a really annoying achievement! I'll have to think about this before I respond with any specific achievement(s), but I will say I dislike the online-only achievements since I don't play online very much :P

I don't remember seeing a trophy like that in Sacred 2. Which one was it?

I'll skip a rant about intentionally "impossible" trophies/achievements, like some in Stanley Parable, or Universe Simulator, only put in because those developers are dicks. (Granted, at least the universe sim guy basically apologized for them later)

As for realistically earnable trophies, the one that sticks in my mind from recent history is:

"Take the Cannoli" in GTA: San Andreas

It's either

a) grinding for hundreds of hours if done legitimately.
b) exploit in a way that involves using in-game cheats and still requiring 4+ hours of constantly walking back and forth and entering a 12 button code thousands of times.
c) exploit it in a different way that involves starting a fresh game, accessing content way earlier than intended to collect unlockables while not shooting anyone (about 4 hours) then holding the shoot button down for 6+ hours once all your prep work is done.

These kinds of trophies are the absolute worst. They're not skill based, just tedious and poorly designed.

I'm not really, what the kids are calling these days, an "achievement whore" but from what I heard, getting the Mile High achievement in COD Modern Warfare was pretty difficult to achieve? Anyone able to validate this?

I've got quite a list of these:

• Killzone 2: Achieve weekly honor rank 1 - You literally have to be ranked #1 for a period of time in the multiplayer base. They also require a 2nd, 3rd, and 4th place trophy as well. It's beyond stupid. Even with online boosting there is no guarantee it can ever be achieved.
• LittleBigPlanet Vita - Arcade Champion - I hated those stupid mini games...so much. A complete waste of time. They could have opted them out and I would have had a better experience.
• Marvel vs. Capcom 3 - Complete all missions - There are so many of these (the trial-type missions for all the move sets) and some of them are impossibly hard. This trophy used to be easier to get when they offered DLC characters, but now you are limited to the base set so that means none of them are skippable anymore.
• Metal Gear Solid 4 - Sounds of the Battlefield - This requires you to collect EVERY title in the game (an 80+ hour task). Some are easy to get, but most of them will require grindy playthroughs or a lot of trial and error.
• Zone of the Enders - Grade A rank all Rescue Missions - This drove me bonkers to get. The first boss you face will actually damage the area you revisit preemptively, so in order to do this properly you have to know beforehand where and how to fight the boss. If you make a mistake, then you have to restart the whole playthrough again. It takes about 30 minutes or so to get back to that spot, but that's really annoying after failing so many times. Even if you can get past that one, A ranking the rest still requires quite a bit of skill.
• Resident Evil 5 - Collect all the BSAA emblems - This wasn't really hard per se, just really annoying and tedious. Super unnecessary.
• Final Fantasy XIII - Loremaster - Collecting every piece of equipment in the game was it's most daunting task. Definitely a time sink. I found this to be rewarding but at the same time monstrously tedius as well.

Also, any/all online specific trophies that otherwise hinder me from a 100% completion. I really wish each game had them as a separate entity...