Kung Pow: Enter the Fist.

Cult classic, but critically panned. Cut together martial arts films, redubbed with added footage for comedy value.

Aside from some that others have mentioned...

FDR American Badass

Some poor taste stuff and a fair bit of racial stuff (though makes sense in that its an over the top comic book satire of a series of ugly characters).

Unassisted or with Riff help?

I'm a huge fan of Ed Wood. His films are masterpieces of bad cinema.

Ed Wood films (in order of preference):
Plan 9 From Outer Space
Glen or Glenda
Bride of the Monster
Night of the Ghouls
Jail Bait

Neil Breen (in order of preference):
Fateful Findings
Double Down
I Am Here..... Now

Tommy Wiseau:
The Room

And of course, Reefer Madness and Teenagers From Outer Space.

Never saw Manos: The Hands of Fate from beginning to end, sadly.

I also enjoy intentionally bad films, like: Zombeavers and Piranha 3DD.

As for "bad" films, I love the Riddick trilogy, Judge Dredd (Dredd is actually great, though), Demolition Man and similar trash!

Rock & Rule
Shanghai Joe
The Street Fighter (not to be confused with the video game series)

I should have added Les visiteurs and Il Mostro in the "bad" films category.

Millennium (1989)

Something about this "bad" movie has an embarrassing grip on me. I'm drawn to the 80's post-apocalyptic, cyberpunk-ish esthetic and the treatment of time quakes and anything to do with plane crashes.

The easy answer is 80s (and maybe 90s) movies like:
The Toxic Avenger (1 and 2, I think after that the movies were just shit, not even funny anymore, IIRC)
Evil Dead
Bad Taste
etc., but I am unsure if those movies really are "bad" because they are intentionally silly, and quite good in their "genres".

I guess the cult-classic "The Room" is not intentionally bad, but I just can't watch it fully. When I start watching it, it makes me uncomfortable to watch, as if the movie was directed (and acted) by aliens who are just trying to mimic how real earthlings live their lives, making it all seem so fake to real humans.

If you see someone watching "The Room" and he is alike "yeah, that definitely happened to me too! Just like real life!", beware, he/she/it might really be an alien in disguise...

There were also lots of porn movies which were very bad as movies, but man they were fun to watch!

Oh, do Adam Sandler comedies count?

I always get a feeling it is popular to hate Adam Sandler as an actor and his movies too, even South Park has made fun of him in many occasions in the history which is kinda a point of no return. If South Park makes fun of you, you are DEAD! D-E-D DEAD!

Yet, I find quite many of his movies quite funny. I e.g. re-watched "That's My Boy" (2012) recently and still found it funny as heck, laughing my guts out in several occasions. I even liked him in "Pixels" (2015).

In fact, the Adam Sandler movies I find less enjoyable are the more "serious" movies from him, like "Funny People", "Reign Over Me" and "50 First Dates" (albeit that last movie had its laughing parts too).

Street Fighter (1994)
Bride of the Monster
DOA: Dead or Alive
Gacy (2003)
Double Dragon (1994)
The Satanic Rites of Dracula
Lara Croft: Tomb Raider
Bleeding Steel
Rush Hour 3
The Knight of Shadows: Between Yin and Yang
Gorgeous (1999)
Bloodsucking Freaks

I can watch any movie with Vin Diesel, no matter how much critics hate it.

I didn't know Tomb Raider was considered "bad".

I second Hudson Hawk and Flash Gordon.

And movies like Sharknado or Braindead are a league of their own, they're simply great and achieve what they're trying to do.

As in movies that you know are bad but you like them anyway?

Every Pauly Shore film.
Super Mario Bros.
Battlefield Earth.
Lavalantula.

I see a few people listing legitimately good films in here though...

Demolition Man is actually misunderstood brilliance, it's a downright prophetic social commentary of then future society.
Flash Gordon is not a bad film, it is intentional, unapologetic cheese.
Beavis & Butthead Do America is just like pretty much all of Mike Judge's work, a crude veneer that hides sharp, biting satire.

Agree with everything you said at the bottom.

My bad movie top 10 (as in, entertaining because they failed so hard):
1. Samurai Cop
2. Battlefield Earth
3. Starcrash
4. Russian Terminator (also known as Russian Ninja)
5.The Pumaman
6. The Room
7. Star Wars: Episode I - The Phantom Menace
8. Future War
9. Plan 9 From Outer Space
10. Death Promise

I love Pumaman, he flies like a moron.

People seem to have strnage definitions of "bad". I'd never call Monster Squad or Evil Dead "bad". Or Flash Gordon. Campy, sure, but bad? Great music, great cast, some pretty good and unique visuals.

I do love DOA. It's truly one of a kind bonkers, fanservice trash. Me and my friends must have watched it at least five times now? It's absolutely the best for a "pizza & beer" kind of evening. If you like beer. I don't, but pizza & DOA is still good enough for me.

Some of my other favorites would be:
Ninja III - The Domination. The title says it all, right? It's the best example of the kind of crazy, awesome 80s nonsense eveyrone tried to parody for a while a few years back, and no one could really get right, because the original is unbeatable and already funnier and cooler than anything they could come up with.

Lifeforce - ok, so, stay with. It's about naked space vampires from Halley's Comet. Where it gets really awesome is it's not really a "B-movie" in terms of production values. The special effects are actually incredibly good. The music, composed by Henry Mancini and recorder by the London Symphony Orchestra, is just fantastic. It really is an incredible movie, has to be seen to be believed, the kind of trashy plot and great movie-making.

Wolverine Origins - it's terrible, but it is also absolutely hilarious. The terrible CG, the nonsense story with the magic memory-erasing bullet, the "could we get Deadpool more wrong?" part, the part where Wolverine gets taken in by Clark Kent's parents... it was one the most fun movie going experiences I've had.