Well, as I partly laid out, there are many criteria for "crappiest".

Offering a finale that doesn't conform to the clues leading up to it is certainly one form of bad storytelling.

Stories that are conceptually bad or just in bad taste is another. Such as HANSI: THE GIRL WHO LOVED THE SWASTIKA. Although that story is about a girl who was indoctrinated as a nazi, and then became disillusioned as a Christian and came to see the nazis as evil. And fronts itself to be a true story.
Or the LOIS LANE story where she becomes black.

Or BROTHER POWER THE GEEK.
Or Simon & Kirby's 1974 offering THE SANDMAN.
Joe Simon's 1968-1978 writing across the board for me is just deliciously out of touch with 1970's readers.
PREZ?
GREEN TEAM?
But bad as these series are, that actually makes them fun to read.

We've discussed it before, for me among the absolute crappiest were Ernie Chan's run on BATMAN and DETECTIVE in 1975-1976. Teamed with writer David V. Reed, and often with inker vince Colletta.

Another contender is Marvel's TEAM AMERICA, which as I recall was to be an Evel Keneivel series, but then he had some scandals, so they did the series with similar characters under another name.

STAR BRAND, and virtually all Marvel's 1986 "New Universe" titles.

Virtually anything pencilled by Sal Buscema. The saving grace on any of his books was an inker who could make it not look like Sal Buscema. Some books he pencilled include MARVEL TWO-IN-ONE, THE DEFENDERS, INCREDIBLE HULK, and ROM.
I actually liked ROM, but more so when Aiken/Garvey were inking it, around issues 25-50.

To a degree, "crappy" is in the eye of the beholder. And books I hate, others look back on with affection, despite arguably not having the greatest story and art. And vice versa.

There's also a "so bad it's good" category. In the template of Ed Wood's Plan 9 From Outer Space.
Jack Kirby's 1975-1976 run on CAPTAIN AMERICA 193-214 kind of fits that criteria.