Stupidity: The Dora Milaje arrive to take Zemo. John calmly attempts to talk them down, but it leads to a huge fight when he puts his hand on Ayo's shoulder. There are multiple instances during this fight where they totally would have stabbed John and Lamar with their spears, and are only stopped because Sam and Bucky intervene. While it's understandable they would want to obtain Zemo, attempting to kill two people to do so is completely out-of-character and goes against all of their morals and principles.
Stupidity: Bucky makes a great show of being about to shoot Zemo...then pulls the trigger with just a click, and drops all the unloaded bullets on the ground before the Wakandans take Zemo into custody. Granted he might have wanted the satisfaction of scaring Zemo, but dropping the bullets a) serves no purpose, because the gun's already been demonstrated to be empty, and b) just makes a mess that he's got to clear up, unless he wants to leave a dozen bullets lying around in a public square.