Stupidity: When Bruce, Betty and She-Hulk are infiltrating Sea-Base, they do so by docking their submarine on top and sneaking in. For what is supposed to be a top secret S.H.I.E.L.D. base, they surprisingly have no security measures - such as cameras and sensors - to detect when an outside force is in the vicinity.
Stupidity: When the Leader's spy is reporting to him, he removes his human mask for the benefit of the audience. This is a pretty foolish thing to do considering he's in a top secret military base, where he can be seen by anyone that happens to be in the area, or potentially by security cameras.