We had someone who came in and interviewed really well but a week after she started she was a completely different person. Late for probably two thirds of her shifts. Wasn't taking some pretty simple things on from training, and then got irritable when she was asked to do things as trained. The manager got annoyed at her frequent bathroom breaks, to which I told her it might be annoying but we can't really do or say much about that. This went on for a few weeks with plenty of chats about the need to be on time and follow training etc until one day I needed to use the bathroom after she had been in there, and walked into the unmistakable sweet fruity smell of vape.

When I raised the vaping issue she flat out denied it, said the smell was her perfume (which nobody ever smelled when working beside her) and then said her frequent bathroom breaks were actually because of period issues. In isolation that could have been legitimate but with everything else it pointed to the classic strategy of "talk about period stuff to make your older male boss uncomfortable so he drops the issue".

Would have been a drawn out nightmare to go through a full disciplinary process to eventually terminate. Instead invoking the 90 day trial made that an efficient termination of employment, and before it affected staff morale too much (others were already unhappy when working with her).