Three come to mind, the first two rage-inducing, the last just really, really disappointing:
1792 Flake - This induced the most visceral reaction I've ever had to a blend. Given where it comes from, it's obviously quality leaf, so I hate to say it's the "worst," but it's the one I hate the most. Unfortunately I tried it not too long after I started smoking, and I didn't fully trust my own tastes. I actually smoked 2 full bowls of it TIRE FIRE. The rest of the tin has been sitting in a jar untouched for 10 years.
Stokkebye HIghland Whiskey - I bought a sample of this in the smoking tent at the 2019 Chicago Show. I got a beer, sat down at one of the couches and loaded a bowl. It had the most artificial, chemical taste I've experienced. Thirty seconds in, I dumped it and gave the sample to another attendee. There are a few PS blends that I love, but this one was terrible.
Peretti B-94 - I wanted to like it, but I just couldn't get past the persistent soapy taste. Why the fu(k does rum-topped cube cut burley taste like fu9king soap? I have yet to find a Peretti burley I like, but B-94 was the one I disliked the most.