Half the stuff here is really highly regarded already and nothing like a cult or underrated classic.
Also a cult is technically less than a minority so you'd need to have a fairly small, yet vocal/passionate fanbase for a movie to be a cult classic. Think some crap like Wiseaus 'The Room' which edgelords jump on to somehow elevate their movie tastes above everyone else - it's a terrible film by any metric but deride it and it's you that's the problem because 'you just don't get it'
With that said, cult classic is used so loosely with movies, it doesn't matter too much.