Self-Propelled Barrier of Stupidity

A non-critical minor character whose sole purpose is to make things harder for the Hero(es) to achieve their goal and cause complications along the way. There is no way to educate, negotiate with or otherwise talk sense to a SPBofS, and this is apparent to the audience from the moment they appear. This is often the abusive sibling or baby sitter. Can also be an uncaring government bureaucrat, the Stupid Boss, or the school principal (when not a key character in the story). A SPBofS need not be in a defined position of authority over the protagonist. Unlike The Millstone, the SPBofS is an outside obstacle, rather than a member of the protagonist's adventure troupe who inadvertently screws things up. Also, The Millstone is usually a more developed and well-rounded figure, with a backstory, etc.

Examples of Self-Propelled Barrier of Stupidity include:

Film

The colossally ignorant older brother in Weird Science.
Dr. Fredrick Chilton in Silence of the Lambs. In many ways, he's the tool's tool - actively confounding the crime-solving efforts of Agent Starling and working toward his own demise at the hands of Dr. Lecter. Although Chilton's death does not arrive by the end of the movie, it's so close we can almost taste it.
In basically every movie where some scientist main character comes up with evidence that a disaster is imminent, those people who ardently refuse to believe him. Often a Commander Contrarian who is likely to cause his/her own death.
In Action films, this will be the FBI if the protagonists are local cops, local cops if the protagonists are FBI, or both if the protagonist is independent of either two groups (if either one isn't the Big Bad or working for them, that is).

Literature

Ed Greenwood is fond of using these as guards in his novels. No matter which protagonist (or group thereof) encounters them, unless they're personally known to these stalwarts they will try to run the 'interlopers' off, arrest them, or kill them outright...anything but check whether they might have actual legitimate business that requires them to move past.