In a couple of his movies, the bad guys are people who take "just doing their job" too far.
Parents are usually depicted as well-meaning, but generally out-of-touch and ignorant.
This is played with in Ferris Bueller's Day Off, where, yes, the adults are easily fooled and/or moronic...but the kids are easily fooled, too. In fact, you could argue that the kids are even more stupid, since (with one notable exception) they all seem to think of Ferris as a transcendent hero, if not an outright Christ figure.
All There in the Manual: Hughes apparently spent several years putting together a detailed history for the Shermer universe of his films (see below), but his stories and notes have never been released. A lot of it wouldn't match up, anyhow (see The Verse below).
Dean Bitterman: Hughes explored this trope twice. In both cases, the principal takes administration a little too far, and becomes needlessly vindictive in dealing with a student.
Principal Vernon from The Breakfast Club is the dramatic version of this trope. At his worst, he tells Bender to punch him, because who's going to believe a useless punk over a respected principal?
Principal Rooney from Ferris Bueller's Day Off is the same thing, except played for comedy. Every time he oversteps the proper boundaries, he suffers a Humiliation Conga.
The Eighties: Most of his best-known and best-liked films were made this decade.
Getting Crap Past the Radar: Some of his earliest films (from before the PG-13 rating was introduced) managed to sneak by with a PG rating, even though their content should obviously have been rated R.
Monochrome Casting: Virtually none of his movies had a non-white lead. Justified, since most of his stories took place in American suburbia, which was still not quite integrated when he began writing.
John Hughes: When I started making movies, I thought I would just invent a town where everything happened. Everybody, in all of my movies, is from Shermer, Illinois. Del Griffith from Planes, Trains & Automobiles lives two doors down from John Bender. Ferris Bueller knew Samantha Baker from Sixteen Candles. For 15 years I've written my Shermer stories in prose, collecting its history.
Weird Science explicitly takes place in Shermer (Lisa is seen teaching the Shermer High gym class at the end), though it has its own Speculative Fiction internal logic that is inconsistent with the other canon Shermerverse movies.
She's Having A Baby does NOT take place in the Shermerverse, since Neal Page's wife is seen watching that movie on television in Planes, Trains and Automobiles.