Joined a new guild on an old friend's invite. One of the first "let's go out and get to know each other" things we did was take my necro up from Rankor to cap FoC. I hadn't gotten around to charging up there by myself yet, but I knew you had to be careful because if he died underground you couldn't use the cap.
We fight our way up there, bs'ing and having a grand old time. I'm just in hog heaven smiling and thinking, "Yeah! I think I can have a good time with this crew!" Totally forgot to mention to any of them the warning not to let him die underground.
What a great first impression - Hi! I know something really critical to our task, and I won't bother to mention it!

The guys were way cool about it, and we did it over. I felt more dumb for that one than any merchant mishaps though.
Second place for me is taking friends out to The Falls as the map expert. No matter how many times I go, even though I know it's there and practically invisible at first, I still always have to run around in a few circles finding that tree bridge.