This sketch from the cover of Simplicity 9597 sewing pattern's packet shows the model for the true hot pants design. The full figure wearing the brown shorts with straps is the only one in hot pants. The others are just shorts.
Both the designs shown above are hot pants. The essential characteristic of hot pants is the presence of braces/suspenders, sometimes with a bib section. The inspiration for this female garment is...
Jawohl! Lederhosen! These German workmen's garments, originally made of heavy leather and designed to fit over other work clothes were meant to be robust protective clothing for doing work involving sharp objects, hot metal or abrasive surfaces. They were both in the familiar short-breech form and in a long-leg form called Bundhosen. In the late 1960's, early 1970's the lederhosen design was adapted to make a type of "active" women's costume. This was a response to the change in societal attitudes which was allowing women to wear leisure wear which was of simple design and exposed their legs and arms to a degree which had previously been proscribed. Patterns were also offered for designs called "playsuits" and "jumper suits" which were single-piece and usually had short leg and sleeve sections.
As with most notorious fashion trends, in practice hardly anyone wore them in real life. Models posed in them, patterns were published, performers wore them on stage and the vast majority of women never even considered wearing them. Here is a very scratchy and fragmented clip from the 1970's TV series "The Partridge Family" in which Shirley Jones shows off the real thing...and some hot pants. To the discerning male eye it looks like they're side-seamed (discovered from the rear view) and made from a light velour fabric. As Susan Dey points out, they "won't wear them in public - only to perform."
The contrived bemusement of the visitors reflects the attitude of the times that they were hot indeed. (The gist of the scene is that they wrongly believe Shirley is making a play for their teenage son and have come to have it out with her).
This photo below, I borrowed from The blog "Life is Dynamite".
This is a jumpsuit, not hotpants. The author comments: "The reason she had to pose on the back porch (I can't believe my dad left the mop in the photo) was because it was 1972 and we lived in Tripoli, Libya. She would have caused a riot if she had stepped out on the street in this little pink jumpsuit." (Well, they've had more to worry about since then...)
The contraption shown below is what is being passed off as "hot pants" today. This is a perfect image to demonstrate what hot pants weren't and aren't: Vulgar, overdone erotica. This is from Agent Provocateur. Well named. If a little more suaveness was evident, e.g. some fabric, it still wouldn't qualify. To be hot pants a garment must have integrated shoulder supports. Suspenders attached by clips, studs, buttons or any other non-permanent connection don't meet the test.
The essence of hot pants was 1970's sexuality; "naughty and nice". The reason for the plethora of micro shorts and simple boyleg shorts that appear if a Google Images search is done for hot pants is good ole GIGO (Garbage In Garbage Out), the computer programmer's maxim which reminds us that electronic circuits only reflect the quality of what is put into them. Those photos have been labelled by people who just don't know what hot pants really were.