In English, we can sometimes use deliberately incorrect grammar for effect in speech. The first example that comes to mind is a more colloquial example:
I ain't never going to do...
When I hear this sentence and the double-negative, it that implies that the speaker is more emphatically saying they aren't going to do whatever it is they aren't going to do (with a bit of added attitude).
Are there any examples in Latin where something that should be incorrect grammar was allowed? It's okay if it's was considered a regional or colloquial usage as long as it would have still be viewed as technically incorrect. There is a similar question asking about known speech errors, although I'm looking more for examples where it was viewed as acceptable to use by some.