Oh hell... I had so many of those playing CoH over the years. Where to even start? The three I remember the best at the moment...
First time the Kronos Titan spawned. Had no idea he was coming. "Thats the biggest Malta Titan I have ever seen! Wait, is he coming at me?! Aack!"
During a Developer-run Nemesis invasion of Atlas Park... I was on my Shield/Super Strength Tank and had her build finalized and decked out in IO's and such. Then suddenly, Nemesis enemies just started showing up... Naturally, I jump into the frey and start Shield Bashing and Ground Stomping my way through them with glee before I suddenly realized that I was pulling a /lot/ of aggro... even for a tank! Apparently, (or, I'm guessing, really) a Dev was watching and was so impressed with how I was doing that they started spawning Nemesis Warhulks right on top of me! o_o;
I wish I could remember how I managed to survive that fight, but I did. Even had a couple of nearby players who saw what happened go 'Hot damn!'
Another time, on that same tank, I was in a mission against a lot of Pretorian Carnies (Carnival of War, faction, I think?) Apparently, they are able to confuse you... They hit me with that and, before I realized it, I had hit a nearby teammate with a super powered Uppercut! They went from nearly full HP to almost dead!
Them: "OWW! WTH?!"
Me: "Oh S#@$! Sorry!"