lapdog: "Playmate of the apes (worst porno ever)"
Now I'll grant you, that was pretty damned bad. I'd love to see the MST3K crew get hold of that one.... but it was made with the intention of being stupid, so I'm not really sure it qualifies. How can a chick who weighs 95 lbs. soaking wet star in a porno?! There's nothing there to see, just a ribcage where you can count every rib! That is erotic?! It was ridiculous, there was like, one decent-looking woman in the whole movie. I am not even a guy and I think this is stupid.
There the other half and I sat, watching the intrepid space-explorers go hiking across the uncleared back lot of some third-rate movie-studio, long hair hanging *below* the helmet-seals of their spacesuits. Ooooooo-kaaaaaay..... ah, the stuff you watch when you've had a few drinks.
That said, that's quite a list you got going there, Odin

I am not sure if you can equate "Mary Poppins" with T2, but its your list, so its all good! Ha....
But.... WORST MOVIE EVER goes to 1994's (? '93, '94.... somewheres in there)..... "THE FEAR". This is about a wooden mannequin "terrorising" a bunch of obnoxious co-eds at a cabin in the woods; its so damn BAD you want to hire the Terminator to show up with his Gatling-gun and waste the whole unlikeable bunch of 'em.
However the idea of offing them oneself is also a tempting fantasy

Charlie's Angel movies also make me want to hurl.
I have heard really bad things about "Feardot.com", but haven't seen it myself so I cant speculate.