It could be the time I was first ever healing with my druid, in Wailing Caverns. Mostly a group I knew(hubby, best friend, his family member), plus someone our friend knew. Made it just fine until the last elemental guy. The 'other friend' died just as we killed the big guy. And he sat there for 5 minutes telling me how incompetent I was, etc. I have only healed one instance since then(and it was BRD with 2 dual-dagger-wielding warriors and we died so many times, I hate that place with a passion). They ruined me and my confidence. Jerks.
See, these 2 warriors were brothers of a friend of our best friend's brother. He invited them to our guild-which we had started simply to stop other people from inviting us to theirs(2 years, going strong, 27 members-4 accounts!). And they expected us to run instances. Only they forgot to mention they had no clue how to tank. So many times in Jin'thalor, Uldaman, the Scourge Invasion, Silithis mini bosses-they tanked, I attempted to heal, I ran out of mana, drew massive hate and ended up going bear and tanking the rest of the fight without problems after they died. Now they tank raids and I do nothing but solo because of them.
Then there was the times we ran WC and attempted Gnomer with Best Friend and his son. Son was group leader. I was on my mage, hubby on his priest. We had no idea what 'need before greed' meant or *why* he put the loot on that. And we couldn't figure out why stuff dropped and we never even got a chance to roll on it! Oh but when cloth dropped, they darn sure didn't pass on it for us! Oh no, and some shoulders dropped that were better than what we were wearing, BF's son(a shaman who instanced *alot*) rolled and won them. I threw a hissy fit until he gave them to me and we left the instance shortly after that.
It was pretty much after that that we swore off instances. Didn't go into SM until Hubby's hunter and my druid could duo the whole thing. Same with others.
Then....there was the time I was grinding AV rep for the Frostwolf. Luckily I was nearing the end but this one guy went on and on and on in chat about how much of an idiot I was for not healing *full-time* and how I should not be allowed in this BG and I should quit right now, etc, etc. I came ><this close to quitting right there. How can someone sleep at night after berating someone so badly. I swear that half the people who play this game do NOT have a conscience.