The worst case is that you vibe code a theorem that reads:

False => P

Then you vibe code a proof of this theorem. Then you get excited that you’ve proven P.

Some of the X discussion that prompted the OP was quite close to this. There are screenshots on X of Lean code that doesn’t compile, with Lean being blamed.

Right, the risk is encoding a vacuously true statement. I consider "false implies Q" and tautologies to be vacuously true statements, since both are truths that fail to convey any meaningful information.

In any case, the worst case scenario is having a vacuously true statement. I picked tautologies as an example since that and statements about the empty set are the first things that come into my mind.