I have one that wasn't actually me, and technically wasn't a game, but was from a TV series and used a game engine.
For those of you who don't know, which I suspect will be many, Time Commanders was a BBC series that ran for a few seasons in the early Noughties (I think it was 2003-05), based around the idea of recreating old historical military battles and seeing if teams of four could possibly do better than the commanders of their chosen army did in real life. Each team was made up of two generals, who were responsible for the overall strategy, and two lieutenants, who were responsible for on-the-ground tactics and would give orders to the show technicians, who controlled the units of the armies against the opposing AI in an RTS style format. The engine used for the simulation was actually a modified version of the engine used in the Total War games, and looks and operates very similar (albeit with improved, more realistic, AI), and indeed The Creative Assembly (TW developers) were included in the credits, though with no mention of Total War itself.
Teams generally proved to be fairly incompetent, with most people losing their battles, though to be fair in some cases their eventual losses were alarmingly close to what really happened. Gamers weren't permitted to take part in the show, sadly, purely because it was thought that gamers would have an unfair advantage against the AI due to possible experience of similar games (which is fair enough when you think about it).
The 'OH SHIT' moment I'm thinking of, specifically, took place near the start of this video:
Yes. That seriously did just happen. The guy charges a massive Roman army with his scouts, leading to an effective Benny Hill sketch type skirmish. The most hilarious part? Afterwards, they claim that it was part of the plan, as they tried to disorganise the Roman troops. Which is the most unbelievable excuse to attack someone since Blair and Dubya claimed there were nuclear weapons in Iraq (oooh, yes, I went there xD).
Also of note is that every team in this series seems to be obsessed with capturing hills. Fine, it's a useful tactic when you need to defend against a tired but large enemy force, or if you're going to utilise a massed cavalry charge, but seriously, the hill is NOT THE OBJECTIVE!!!!!