I applaud Paradox's attention to detail. Look! They even included Atheists.
More of a moment that made me go "&#%$!" than "What?!" was a series of wars I had as Tuscany. Modena was my vassal, but the chance of Modena accepting annexation at this point was "unlikely". So, to up my prestige and pass some time, I declared war on Genoa, whose ally I soon found out was Venice. This was around 1465 or so, so I had already annexed a few of the surrounding one-province nations. No biggie, I could take Genoa and Venice on with my ally Modena. I was right. The only way I got peace, though, was by annexing Corsica and two of Venice's territories on the peninsula.
That war lasted about two years or so, and had drained me of all of my manpower just to subdue the Venetian army. Here's where the "&#%$!" moment comes in-- with 0 manpower left, a drained treasury, and a couple of provinces with a medium probability of rebellion, Aragon, along with her allies of Flanders (Calais rebelled earlier) and Austria (oh crap) declared war on me mere
days after the peace with Genoa and Venice was sorted out. I sent almost all of my army south to defend my border with Aragon (who had previously annexed part of Sicily), but sent a small force to Corisica and another to the east coast to ward off any possible Austrian landing. I manged to hold off the Aragonese for four years, even capturing Corisica and defeating two of her armies and the whole time I
still had 0 manpower to get more troops. And those infernal Aragonese would not give up for anything! I controlled one of their provinces, had defeated all of their advances, and yet those dagblasted Aragonese
would not surrender! They eventually accepted an offer of 25 ducats from me for peace, sending me into debt and forcing me to take a loan.
And that's when the allied powers of Sicily and Savoy declared war on me.