Hmm. The picture describes a threat, not something you wish you had done. So, if a parent says to a child, "Don't jump on the bed or you'll wish you hadn't", it means that the child are going to get severely punished if they jump on the bed.

That is a perfectly fine sentence. It illustates a mature attitude toward the necessity of preparation. We also use this structure in a cautionary sense (not threatening), as to a friend who doesn't want to do something. "I think you will wish you had (done so)"

Hi Arkadiusz, yes, this is an example of a first conditional sentence, where you predict a likely outcome in the present or future. The structure and meaning both make sense.

Unless someone else has threatened you....but you would have to describe that situation in order to read threat into it.

Oh right. No, it's no threat at all.