The worst by far I've ever used was on a circa-2007 HP convertible laptop that ran Vista. Despite it costing more than some models of MacBook at the time, the thing was built with that cheap creaky "fake metal" glossy plastic, and that included its trackpad. The trackpad would've been bad enough just like that with the smooth plastic gripping at your fingertips, but to make it worse its surface had inverse dimples, and because its touch sensitivity wasn't all that sensitive you had to apply more pressure when using it which pressed your fingers down into the dimples and made them stick even worse. Oh and of course, as was customary for non-Apple laptops at that point it was also tiny.
It's almost as if it was someone's job to make that thing's trackpad terrible to use. Just mind boggling.