When the enemy AI suicidially rushes you, especially throwing grenades, to deal any damage. Meanwhile, I have limited ammo and grenades but I can’t get new grenades from enemy soldiers because they use them up on me.

Stellaris has gotten especially bad with pacifist empires building huuuge fleets that just hang out during peace time. Then they go all in on the next war that they are overprepared for, even though they could not possibly predict it. And they fight like rabid wombats, not rabbits.