Bob is entering his first day on the job at Trope Co. Industries. He expects to spend the first few days getting his feet wet, learning what his responsibilities are, getting to know his co-workers.
And before he can really get settled in, all hell breaks loose. Criminals break in and take hostages. Massive equipment failures. Aliens invade. War breaks out. They run out of coffee and can't get more until tomorrow. Bob then either takes up responsibility for dealing with the crisis or the responsibility is already part of their job. No guarantees they're up to the challenge.
Distinct from It Never Gets Any Easier, in that this is clearly not part of the routine. Compare with New Job Episode. Contrast Retirony ("last day from hell").
In Men In Black, Jay becomes involved in a plot to save the galaxy within his first day or so. While Kay *tells* him that It Never Gets Any Easier, that's hard to believe, and what we see of daily life for MiB does make it seem constantly crazy, but not always as high-stakes as when the bug was pursuing the galaxy.
Gwen Cooper's first day at Torchwood starts with a meteor hitting Cardiff, moves on to Gwen accidentally releasing an alien being, and progresses to serial murder and alien possession. Because it's Torchwood, the job never really gets easier.
In Babylon 5, Delenn's first day as a full-member of the Minbari Grey Council was the day the Minbari encountered the Earth ship Prometheus. An encounter that resulted in the botched first contact-turned-battle that killed Delenn's mentor, Dukhat, and sparked the Earth/Minbari War.
Lyta Alexander is the station's first certified Commercial Telepath. Her first day on the job involves an assassination attempt on the Vorlon ambassador, her having to scan the alien ambassador's mind to find who the killer was, and ending up falsely accusing the station's commander as a result of what she was mislead to see in the scan. She gets transferred off the station soon after the incident.
Captain Sheridan arrives on the station and has what is, by the standards of B5, a relatively sedate example, as a rogue Minbari warship attempts to goad him into firing the first shots of a new war between Earth and Minbar (Sheridan was a hero of the previous war, which ended under very odd and unexplained circumstances).
Captain Lochley's first day as station commander involves a plot to assassinate newly-inaugerated President Sheridan (making this a two-fer, given that it's Sheridan's first day in that job as well, though he's hardly new to the insanity that is life on Babylon 5).
In 24, Lynn McGill's first day as head of CTU Los Angeles involves getting mugged by his junkie sister and her boyfriend, leading directly to a nerve gas attack on CTU headquarters. Which gets him killed.
In The Sentinel, Blair's first day with the police includes the entire police station being taken over by terrorists who take him hostage.
Anthony Nowakowski's first day in Oz as a correctional officer fell on the same day a riot took place in Emerald City. He was killed by friendly fire after Devlin sent the SORT team in.
The Suburban Jungle's sequel comic, Rough Housing: Charity's first day as manager of The Rough House has her find out the place is a ramshackle dump, most of the employes work for room and board in lieu of pay and the only thing keeping the place afloat is a weekly free-for-all (highly illegal) barfight... Which happens to be that night.
Thomas the Tank Engine & Friends: Poor James. On his first day, the Troublesome Trucks decided to be hard on the new engine and pushed him down Gordon's Hill. His outdated wooden brake blocks were set alight from the sparks thrown up as he tried desperately to stop, and he wound up crashing in a pasture.
Ben Sliney's first day as the FAA's National Operation Manager (basically the Air Traffic Controller-in-chief) was September 11, 2001. It was his call to ground every civilian aircraft in America for four days (over 4,200). He played himself in the film, United 93.
A frequent occurrence in the service sector: First day behind the register? In comes an armed robber. For example...