Two stories.

First, the worst hiring experience: I interviewed in February. Not a phone screen - a full, in-person interview. It went well. But then the company had a hiring freeze. I was hired in, IIRC, September. Six months from interview to offer. That was not particularly anybody's fault, but the circumstances worked out badly.

Second, the worst on-boarding experience: On Monday, I got a cubicle and a badge. On Tuesday, I got a trash can. On Wednesday, I got a computer. On Thursday, I got network access. Why was it that way? Because the hiring manager was on vacation the week I started, and forgot to delegate the job of getting me set up to someone else.