The whole point of a mentor is to ensure that the protagonist's transition from Naïve Newcomer to The Hero goes smoothly. Admittedly, sometimes this is impossible, depending on the setting and situation. A mentor in an office has considerably more power to make things easier on his/her intern protege than a warrior mentor has to lighten the burden on his sword-swinging student. Sometimes, the teacher may decide they have to be cruel to be kind, in order to hammer home An Aesop about their charge's new responsibilities. Even if they do though, they have their student's best interests at heart, and will step into the firing line themselves in order to protect the rookie, sometimes taking responsibility for their mistakes. Whether that means taking a bullet for them or facing a board of inquiry varies from setting to setting.
The protege will probably be aware of this, and even if their teacher initially drives them to frustration, they will come to appreciate and respect the many sacrifices made for them by their mentor.
And then you get the poor saps who are stuck with this guy.
This mentor sees their charge as an amusement at best and The Millstone at worst. They make little or no special effort to adapt to their student, carrying on the same as they always did and expecting the newcomer to keep up. Often, they are there to illustrate why experts can make the very worst teachers, since they're usually very good at their job, but terrible at teaching someone else how to do it. Only the most determined, talented and self-motivated (or just plain masochistic) characters will survive apprenticeship to the Fair Weather Mentor.
And even if you do... don't think you're home free yet. The very definition of this mentor is that unlike his self-sacrificing and responsible counterparts, he will drop you like a hot potato the very instant you mess up. In fact, he'll throw you into the firing line if he messes up. His protege is nothing more than a tool or an inconvenience to him; his own career and reputation will always come first.
Sometimes, the effectiveness of his strategy defies belief. For example, the police officer who leaves a rookie in charge of a dangerous suspect while he pursues another target comes back to find the hapless newbie knocked out, and the suspect long gone. When they're pulled up by their superiors, it's the newcomer who gets blamed. No-one ever stops to question the wisdom of leaving a green recruit in charge of a dangerous criminal. Somehow, the Fair Weather Mentor always seems to have an elitist, or plain incompetent, hierarchial system backing him up.
If, by some miracle, you manage to succeed under the tutelage of this mentor, then he will be quick to take credit for your success, having "taught you everything you know." You'll never really be able to rest on your laurels though. Even years after you've left their care, one false move will result in a phone call to inform you that you've been disowned. This mentor often appears in video games, as a means of enforcing a Non-Lethal K.O.. This also explains the bizarre systems backing up this irresponsible character, since it's justified by the Rule of Fun.
Often overlaps with the Trickster Mentor (hope you've got a good therapist), or even worse, the Sink-or-Swim Mentor (hope you've got a back up career plan... or life insurance). The most painful examples of Fair Weather Mentors though, are those that seemed funny and kind right up until the moment their student made a small mistake... whereupon this mentor humiliated them and abandoned them.
Compare Mooching Master, who exploits their student's finances instead of their reputation.
- Nagisa, in Loveless, is one of these, explicitly telling her second set of Zero fighters (Yoji and Natsuo) that she didn't want them if they lost a battle. She ends up taking them back after her first set of fighters, Koya and Yamato, quit spell-battling and cut their ties to her. She also practices a strange sort of Parental Favoritism that shows that while she has at least some genuine regard/affection for the Fighter of the pairs (and thus cares about their welfare), she states bluntly that she hates Sacrifices.
- Happosai in Ranma ½. His training regimen consisted of abusing and exploiting his students, then letting them get blamed for his crimes. At one point, when an old adversary came to get revenge on him, Happosai tried to blame Ranma for his actions (never mind that the crime was committed over a century ago and Ranma is only sixteen).
- Genma Saotome fits this list too. While he seems to have been a lot less abusive then Happosai prior to the series, and he does still try and train Ranma seriously when he bothers, Ranma's concerns and safety take a pretty distant second to saving his own skin. A good number of all the problems Ranma has to put up with is trouble Genma stirred up that he makes Ranma deal with.
- General Cross is this to Allen Walker in D.Gray-Man. He taught Allen to be an exorcist by throwing him into dangerous situations with little regard whether he survived, was a compulsive gambler who had a habit of running away and leaving his massive debts to Allen - so massive that simply mentioning them can make the ever-cheerful Allen teeter on the edge of the Despair Event Horizon - and when he decided Allen needed to head to headquarters, he knocked him unconscious and ran off, telling Allen to make his own way there.
- In My Hero Academia, Sir Nighteye begins as this for Midoriya, having only taken him on to destroy his self esteem and convince him to give One For All to Mirio. That said, he begins to warm up to him in time and defends Midoriya when Nighteye's order to not rescue Eri ends up complicating things in the long-term. But in the end, the damage from their first impression is done, as Midoriya is nearly convinced to hand One For All to Mirio as Nighteye wanted and is only dissuaded when Mirio himself refuses.
- Lucien Draay from the Knights of the Old Republic comics. The rest of the First WatchCircle isn't much better off, since the Jedi Tower on Taris and their Padawans were essentially a cover-up for their secret activities in the Jedi Covenant, but at least the other four Masters actually put effort into the training of their Padawans, while Lucien treated Zayne basically as a nuisance and a source of cheap laughs. It was also implied that he had no interest in training a Padawan at all, and used Zayne's Force disability as a excuse to ignore and not seriously train him. It's telling that Zayne Carrick become a skilled Jedi after he went on the run to clear his name for the crimes Lucien framed him for.
- The First Watch Circle Jedi Masters were this to their Padawans. While it's true that Lucien was the worst of them and at least the four other masters actually put effort into the training of their Padawans, it is clear they only took Padawans in because they had no choice, as they needed a cover-up for their secret activities in the Jedi Covenant. When they get a vision they believe shows them one of their students turning to the Dark Side, they decide to kill their students. How they react to the thought of killing their students varies. Raana Tey was the first to say they should kill their students, though later she would suffer from guilt. Lucien Draay and Feln are indifferent to the thought of killing their students and show no remorse. Q'Anilia and Xamar are the ones most horrified at the thought of killing their students, but reluctantly agree to kill them. Both Q'Anilia and Xamar suffer a tremendous amount of guilt for the murder of their students, but only Xamar questions if they did the right thing and finally confesses to their crimes.
- Nathaniel in The Bartimaeus Trilogy gets stuck with not one, but two of these: Underwood, who not only fails to shield him from Lovelace's verbal and then physical attacks, but fires the woman who did try to help him, and Whitwell, who lets him know in no uncertain terms after the ransacking of Gladstone's tomb while Nathaniel was in Prague that even if he somehow salvages his career, she's finished with him. Small wonder he turned out the way he did.
- Also by the same author is Agent Jacobs, Lucy's old mentor, in Lockwood & Co.. A childhood spent going against ghosts have made him jumpy and nervous and cowardly. His refusal to help his agents in one disastrous case leads to Lucy's friends and fellow agents dying, and in the inquest that came up afterwards he claimed not to be able to hear them screaming or calling for help. Worse still, everyone expected Lucy to go back to working with him. She doesn't; she heads to London instead.
- Ripred from The Underland Chronicles could fit into this, particularly in Gregor and The Curse of the Warmbloods.
- This is one of the first things to separate Dr. Kelso from Dr. Cox in Scrubs: Kelso is a Fair Weather Mentor, polite and charming to new interns...until they mess up, whereupon he scolds them and leaves them to their fates. Dr. Cox is acerbic and a bit of a Sink-or-Swim Mentor, but is also a good teacher who tries to protect and help his students even after he is no longer obliged to, looking after J.D. in particular even after he becomes the hospital's (co-) Chief Resident.
- One episode suggests that J.D. is the first intern Cox has had this sort of patience with; Kelso tells him that the reason there aren't loads of mini-Coxes running round the hospital is because the second they question him, he drops them. Whereas with J.D., Cox takes a step back, and explains what he was trying to tell J.D. better.
- Merlin is this in Interstitial Actual Play. He actively causes problems for the party under the guise of helping them find information on the Organization, but when he finally does actually tell them things it's only stuff the party already knew, and him tasking them to go to other worlds and stop the Organization is redundant because that's what they were already doing. The only reason they stopped near him was to get gas.
- Shawn Michaels, as described by CM Punk, particularly when it came to Bryan Danielson, who Punk accused Michaels of merely taking money from. Shawn's training as described by London and Kendrick also seemed rather...sparse. In his defense, Michaels has been shown to be very supportive of Danielson later in his career and may have been playing a Genghis Gambit on his students.
- Amber O'Neal claimed Amanda Rodriguez as her trainee but after O'Neal was recognized by Bullet Club as an official member she beat down Rodriguez in front of them at a SHINE event to demonstrate how to "squash" a rookie. Even when Rodriguez found some success as una Sicaria under new mentors Ivelisse Vélez and La Rosa Negra, she was cut off again by O'Neal, who joined C4, a group dedicated to destroying Las Sicarias. As it became clear C4 couldn't beat Las Sicarias in a fair fight, O'Neal lured Rodriguez back under her wing by preying on dissension between Rodriguez and Thea Trinidad.
- In the Nintendo DS game Lifesigns, both Dr. Tendo and Dr. Aoshima are under the care of Suzu-sensei. Newcomer Aoshima complains that Suzu places her in the care of Tendo (a trainee!) rather than taking responsibility for Aoshima's tuition herself, but Tendo explains that's just how their teacher does things. More worryingly, he mentions that Suzu got angry with him every time he asked her for help in his first year. So far, Suzu has only shown herself to be a Sink-or-Swim Mentor...but over the course of the game, she makes it clear that she will accept no responsibility for the actions of her interns, even when she herself forces them to do procedures no sane doctor would let a rookie do.
- Sawai pulls it to a degree as well, telling Tendo, his own son, that if he makes even one mistake he'll make it so that he'll never work again.
- Another DS game, Phoenix Wright: Ace Attorney uses such a mentor as a plot point. Manfred Von Karma trained both ace prosecutor Miles Edgeworth and Karma's prodigy daughter Franziska. General opinion is that Von Karma was a tough teacher, but he seems happy enough to be acknowledged as the man who trained the "Demon Prosecutor." However, when Miles is accused of murder, Von Karma is quick to prosecute his former student and disown their teacher/protege relationship. Of course, Manfred has a highly convoluted and chilling reason for this turn of events... Which is because von Karma was the one who initiated the set up so that he could get revenge on him for what Edgeworth's father had done to him in court over 20 years ago (which was a penalty on his former perfect record). von Karma sought revenge on the Edgeworths and by killing the one who soiled his record, turned the guy's son into the opposite of what his father wanted him to be (from defense attorney to prosecutor), and then get the son accused of murder years later, it would have been Karma's perfect revenge. A subversion as well too; von Karma is shown to be a pretty normal father, and he's only really a hardass when it comes to the courtroom.
- The player is more-or-less this in NetHack. Pets can be extremely useful for support in combat they can help you identify safe items to wear and use and can steal from shops for you, in exchange for making sure they have a steady supply of corpses and easy kills to level up with. But they're also somewhat expendable—you'd like to keep them alive forever and it's a blow when you lose a good one or your last one, but there's many situations where the proper course of action is to let your pets die to save your ass (such as if a level drainer gets too close for comfort, or if you're starving to death).
- In Baldur's Gate II, a mage's stronghold quest involves the player character being blackmailed into tutoring two students and a douchebag. You have the option of playing this trope yourself.
- Telvanni Master Wizard Neloth is one to his apprentice, Talvas Fathryon. Asking Talvas whether Neloth is a good teacher results in Talvas replying that while he is exactly as powerful as he claims to be, he mostly sees Talvas as a servant, teaches him almost nothing and cruelly punishes him when he fails.