Everything.
While in the hiring process for a role I had met with my potential manager and was hired verbally and was assured I would have my offer letter meeting my salary requirements by EOD, as I was offered another role at a different company which required a response.
I did not receive an offer letter by end of day, nor the following, or following- you get the gist. I was assured it was coming after several requests and once it was finally under submission, I was informed they'd be cutting my agreed upon salary by $15k and assumed I would still be accepting the role.
I have never experienced a more unprofessional company with such lack of communication and disrespect for potential employee's.