Personally, i do not believe that what you made is the “worst roblox game”. I believe that making the actual worst roblox game then it would require a more specific game design philosophy to be used.
Other than unfun gameplay, what else you could do to REALLY lean into that bad game category would be:
Use absolutely the least efficient code possible with the worst possible design in order to maximize average horrible performance, create stutters, potentially create crashes, memory leaks, etc…
Make the server as inefficient as possible, same things from the point before can be applied.
NPC Ai is somewhat hard to decide over, the ai could either be insanely powerful to the point its just “unfair” rather than “bad” ai or you could use some really crappy npc ai that would actually be considered “bad”.
Clutter the screen with as many useless things as possible. Random giant neon buttons asking you to buy some random gear, random robux purchase prompts (make them cost like 999999999 robux ofc), ugly click effects, etc…
Potential place teleporters (that are way too easy to access and should be able to fool players into initially thinking that those arent actually place teleporters)
Free models from 10 years ago ofc
I believe there may be many more things that could be done to make the game even worse however these are all the things i could cope up with at the moment.