I'm sure there are quite a few that we could put here. Here are 2 that come to my mind.
Alienator (1989): I saw this on a second-rate premium channel that showed "action" movies, mostly krap like Time Chasers. This has all the cheese you'd expect from a MST3k movie, including a steroid-pumped female (she-male is more like it) android assassin that looks kind of like pro wrestler Chyna with blonde hair. I think the reason it didn't get MSTed is because of the constant F-word usage.
Troll 2 (1990): I only saw the last few minutes of this but I could tell that it was realy dumb. In fact, in the Internet Movie Database's Bottom 100 movies, this one is all the way up at number 7! If it's as bad as the user comments say it is, it could have easily made the funniest MST3K episode ever.
Has anyone seen The Car? A demonic vehicle terrorizes the roads of a dessert town in what's supposed to be a horror flick. Oh, and there's some sort of curse somehwere, I think. Man, this turkey has MSTing all over it.
I've watched a few of the more recent Amityville movies (Amityville Toyroom, Clownhouse, and yes, Karen) on Tubi. The MST lot would have a field days with these, as they make Plan Nine From Outer Space look like Citizen Kane.
Most of these movies have nothing to do with the Amityville Horror, aside from using the name. You could take away all the Amityville references and still have the same movie (not that it would improve said movie in the least).
And the production values: YE-IKES! A few of them look like some class project. Like they filmed at Joe Schmoe's house and then edited the movie on his computer in the basement.
And a few of these movies make Amityville seem like some hick village in the middle of nowhere, complete with rednecks lurking in the woods. In reality, Amityville is on the south shore of Long Island, within driving distance of New York City. A long way from any rednecks.
The only saving grace is that these movies clock up at only an hour and fifteen minutes. Because that's time you'll never get back.
I'd say the Sharknado series, but that's just too easy...
Rifftrax did the first 2 Sharknado films. Probably the only way they're watchable. ;-)
The first one was in the "so bad it's funny" category, so I could handle it.
They actually made six of those movies.