Let's start off with an easy one. HBO's Game of Thrones, specifically the Long Night episode.

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This whole episode is full of all sorts of problems. It looked cool, but in a military sense, especially with all the capable commanders there, it was awful. Their cavalry should've been on a flanking position or dismounted behind the walls instead of charging alone into the enemy, which in turn only feed their ranks. Same goes for the Unsullied, who probably should've manned the walls, and all those catapults/trebuchets they built. If they were pressed for time, why would they leave all that siege equipment they had to spend time building on the front lines instead of behind the walls where it would at least be safe to use until the dead breached the walls? 

There was also that pitiful trench, which they could've dug deeper and spiked it with dragon glass or at least sharp sticks to slow down the enemy, but even then they could've spared some to tip the edges. Plus it would've caused more dead to burn up when the trench was lit, surely.

I'd also complain about the crypt scene, which should've honestly been left out. Yes, it's cool and adds to the horror and drama, but are you seriously going to tell me that rotting corpses that have been there for hundreds, if not thousands of years are capable of punching through thick stone? It made no logical sense.
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