Paranormal activity.
Horrible, just horrible, it wasn't scary, it was stupid and boring. They didn't even research how does these things work. there are countless of real cases with no explanation, books of esoterism, but no, they did something extremely basic and common. Also the sequels were the same as the first one, really nothing "new", same situation but with other characters.
I'd mention the REC movie (I watched both versions), sometimes it was scary but it was the usual jumpscares so it wasn't "that" scary, it was more the surprise than anything else, and I was more concerned like "why don't you just do something else instead" "why are you separating in a closed place with potentially 2 crazy guys hidding somewhere and you're all with NO weapons?!". Oh and the Resident Evil, the first one was "ok" but later they went full Michael Bay with Matrix and who knows what, it stopped being a zombie survival and became a X-Men zombie survival. I didn't like at all Silent Hill 2, the first movie kinda followed the plot, kinda, and I'm grateful of that cause they could have messed up and the fact they changed Harry for his wife instead... at least it kinda followed the point of it, but the 2 was...something made for teenagers, yeah, I liked the pyramid head and that they kept the monsters AND the OST. But still, the 2 had potential from the game to make an horrific movie, you know, could have been better.
But I still think the worst are Paranormal Activity, REC and Resident Evil. YEP.