I don't think that I can give the worst, but I can give some that I did not enjoy.

• Invisible teleporters. Some old RPGs

like the D&D Gold Box games

came without an auto-mapping feature. Part of the game was, as one played along, manually creating a map on graph paper. This in-and-of-itself was somewhat time-consuming, and if one made a mistake or got turned around, it could be hard to fix one's map. A particularly obnoxious feature to complicate this was that sometimes, there'd be unmarked teleporters to move you to another place on the map without notice, and you had to figure out that this had happened. Very annoying. I didn't like this mechanic.

• Real-time games with an intentional omission of a pause feature. Some strategy games do this. The idea here is to force you to think in real time, and not permit you to just pause and think about things. Problem is, even if one agrees with this, in the real world, sometimes you need to answer the door or use the toilet. Not a good idea.

• In general, positive-feedback loops that increase the difficulty for the player. An example would be shmups where being hit causes not just the loss of a life, but the loss of a level of one's precious weapon power, or something like that. That means that when one is doing poorly, the difficulty also ramps up. There's some degree of this in many games insofar as it might be harder to play when one is weaker, but in the shmup case, I really don't think that it's necessary

a game would be perfectly playable without that element. I don't really like situations where it's just added for the sake of being there.