if you do it once, it's good. If you do it twice on the same day, it's a serious crime. what is it?

One possibility is getting married (to different people). However, both don't need to be done the same day to be a crime.

I hope this helps. Thanks for asking.

The statement you provided is a riddle and the answer is not specific in the context you gave. However, based on the given information, one possible interpretation is that the answer is "counterfeiting money."

Counterfeiting money is illegal and considered a serious crime. If someone were to counterfeit money once, it may be seen as a lesser offense, but if they were to do it twice on the same day, it would be considered a more serious crime due to the repetition and intent.

It is important to note that counterfeiting money is illegal in most jurisdictions and carries severe penalties, including imprisonment and fines. This explanation is for educational purposes only, and I do not endorse or encourage any illegal activities.

If you have any other questions or need further clarification, feel free to ask!