When the movie mocking show MYSTERY SCIENCE THEATER 3000 went off the air in 1999, it took a few years for the cast and crew to get back into the saddle. For Mike Nelson, Kevin Murphy and Bill Corbett, they eventually started The Film Crew. The premise was slightly different (three guys working for a DVD production company forced to make commentary tracks) but the result was the same (three guys watching bad movies and keeping their sanity with the help of their pointed barbs). However, the Film Crew DVDs got held up and in the meantime Nelson started Rifftrax which cut out the surrounding premise and solely featured comedians making fun of movies. For this straight-to-DVD release, the film is a fairly infamous public domain feature.
Roger Corman's THE LITTLE SHOP OF HORRORS (1960) is a deliberately silly, campy romp with over the top characters, surreal situations and nonsensical, non-realistic dialog. The main plot concerns a meek and weedy clerk who grows a giant man-eating plant in order to win the affections of a rather dull and ordinary woman. More by accident than design, the clerk manages to keep his creation fed with increasingly random members of the local population until finally the plant's appetite for blood cannot be contained. I wouldn't go so far as to call this a bad movie; it is what it is. It's not intended to be taken seriously and so I found it a little difficult to fully take the mocking in the spirit in which it was intended.
LITTLE SHOP probably works better as a stage play (my only previous experience with the work was via a high school production many many years ago) and the film production certainly has its issues (the typical Corman low-budget being at the center of many of them). However, as MST3k alumni Frank Coniff noted at the MST3k 20th Anniversary Reunion Panel at Comic Con, it isn't terribly easy to riff on something that is already a comedy, even a bad one. To paraphrase TV's Frank, one usually just ends up yelling "That's not funny!" at the failed jokes.
Unfortunately, Coniff's point is reflected in a fair amount of the jokes aimed at LITTLE SHOP. That said, there are still a lot of funny quips, some of which are right up there with classic MST3k material. I don't know if it was my imagination, but it seemed to get much better in the second half. So my only advice is that if you initially find the jokes to be a bit dull and listless, just be patient.