Fantasy Mission Force
Jackie Chan's most surreal film, which he only appeared in for about fifteen minutes of total screen time, as a favor to its lead actor for saving his life from the Triads. It's downright bizarre, and should provide you with lots of great material.
I just saw this for the first time. OMG is this a gem, you could watch a thousand bad movies and not catch one as amazing as this!
Please riff this freak show already!
As an added bonus, I believe this movie is in the public domain in the USA. (At least, it shows up in every public-domain Jackie Chan movie repackager's line of cheap Chan movies.) So they could do it as a VOD, not just an audio track.
(I hope they'd go ahead and snag the import version on DVD so they could do it in letterbox rather than the pan and scan those collections usually get.)
Rory Simpson commented
At no point in this film did I understand what was happening. It may be too unintentionally funny to make it work, but I trust the riffers to ascertain it's potential given their experience in this regard. It is really epically awful and completely b@tsh!t, and even if you dont riff it it's worth a watch.