The worst for me was during Guild Wars. If anyone plays this, you know how maddening it can be trying to get Obsidian armor from the armor crafter in FoW ( which btw you have to accomplish a couple of hard quests while protecting this character to actually reach the armor crafter ).

So, our group finally pulls up to the armor crafter. Me and two other players were getting their Obsidian armor crafted by the armor guy. The thing with these armor crafters is that you have to click on the piece that you want, such as chest, legs, etc. and each piece has its own requirements to achieve it. It's nothing big, until one our players somehow manages to accidentally aggro a group of enemies which come charging right at us. I panicked a bit and accidentally purchased the same piece twice. Now, it's not a big thing here...but let me tell you that the items to craft these armor sets are insanely rare and grotesquely expensive...and let's not forget the fact that you need over a 100 of these items just to craft one piece of the set.......
I cursed that player, and myself for being stupid.

It took me a month to return and get the full set. T_T