There are loads of terrible Star Wars games. We've talked about them here before. But there's different reasons someone can say a game is terrible. They might not like the genre, or the platform, or the way the game has treated the Star Wars canon.
One thing many will agree on, though, is that the absolute worst Star Wars game ever made was 1997 disasterpiece Star Wars: Masters of Teräs Käsi.
Taking its name from a style of unarmed combat present in Star Wars' expanded universe, Teräs Käsi was a PlayStation fighting game which looked a bit like Tekken, but sadly played nothing like it.
Using 3D characters in arena-style stages, Teräs Käsi concoted a flimsy plot about an assassin hunting down the Rebel Alliance to construct a fighting game in which players could make Chewbacca fight Darth Vader, Boba Fett take on Han Solo or, well, just about any other combination they could think of from a roster of 12 characters (actually 13, but Leia's in there twice).
At the time, it wasn't received too poorly. And you'll still find today people saying "oh, it's not that bad". Ignore them. This game was offensive on all levels.
As a fighter, it was terrible in that it was slow, clunky and unfairly balanced towards characters with lightsabers. As a Star Wars experience, it was even worse. Not that "breaking canon" is something only this game can be accused of, but man, this was extra stupid. Not even the inclusion of Slave Leia as a character could save it.
My biggest gripe at the time, though, was how much of a waste it was! How it could have been something actually worthwhile. It was developed in-house by Lucasarts, the team behind some of the finest 2D pixel art the world has ever seen. Even in 1997 (well, 1998 for me, since that's when it was out in PAL territories), it seemed ridiculous they'd try - and fail - to make things 3D when a 2D fighter would have not only looked better, but also presumably have been easier to make as well.
Sure, you can say "well, it might not have sold as well", but hey, this game didn't sell well. Because it was terrible!
Oh, and before we go: if you say "no, Star Wars: Rebellion" was the worst game, I will probably ban you, because such talk makes me very upset.