Being Personal Isn't Professional

There's someone you know at work. They're professional and polite, always making a good first impression. They're very good at what they do, but take everything way too seriously. They're quick to introduce themselves to everyone in the workplace, but don't bother to find out any more than their co-workers' names and strengths within the workplace. It's not uncommon for people to start wondering if they are a robot due to their lack of extreme emotion and aloofness. If a situation arises, they will usually help out the one in trouble, then later brush it off saying Think Nothing of It.

One day, you happen to run into them outside of working hours. Not only do they greet you with a large smile on their face, but they are actually quite lighthearted and talkative. Turns out, they are rather social, but not at work. They might even be wild, flirty and hate the persona that they're forced to show at work, especially if they're a Stern Teacher or Drill Sergeant Nasty. However, once they return to the workplace, they've returned to being as social and friendly as a rock.

Truth in Television, being too emotional in certain jobs may prove dangerous or at least detrimental to how well you do the job.

Compare Sugar and Ice Personality, which occurs when a character is cold to the world at large and only exhibits their softer side to certain other characters.

A sub-trope of Work Hard, Play Hard, where a character is a hard worker and a huge party goer, but doesn't always draw a strict line in between.

The Consummate Professional is very much likely to subscribe to this trope. Compare Hates Small Talk.

Anime and Manga

 * Ebisu from Ebisu-san and Hotei-san is like this as she tells Hotei that she doesn't have time for personal conversations at work because Ebisu's firmly committed to not putting in any overtime.
 * In Virgin Love, Daigo purposefully keeps his work persona and his true personality separate. He's generous and easy-going by nature, but as a young CEO has to be professional and commanding at all times in the workplace to ensure the company's survival.

Literature

 * Mr. Sturgeon from Gordon Korman's Macdonald Hall is like this, he is so strict that he's known for his 'fishy stare', yet funny and good humoured to his wife.
 * John Wemmick from Great Expectations is like this. At the office of Mr. Jaggers he's a humorless, slightly unpleasant man who is devoted to the acquisition of 'portable property', while at home he is a joyful, caring, and generally amiable fellow who lived with his ancient father in a whimsical house built like a tiny castle. He's very insistent that his personal and professional lives don't cross.

Live Action Television

 * Spoofed mercilessly with the character Wayne Jarvis in Arrested Development.
 * Michael Weston of Burn Notice can be like this.
 * Dr. Clark Edison on Bones. He really doesn't want to be involved in anybody's personal life and is less than pleased with all the interpersonal non-business talk.
 * Until he opened up. His new problem? Oversharing.
 * The Thin Blue Line, where Inspector Fowler can't give opinions as both a commanding officer and a boyfriend at the same time.

Newspaper Comics

 * In Calvin and Hobbes, Calvin is surprised to hear his mom ran into his teacher at the store during the summer. When asked why he said he had always imagined that teachers spent the summer sleeping in coffins.

Video Games

 * The Sniper from Team Fortress 2 insists that his feelings don't enter into his job—there's no room for them. "Professionals have standards."
 * Nel from Star Ocean: Till the End of Time. She goes on and on like a broken record about her mission. But the second part of this is true too, as when Tynaeve and her other friend are kidnapped, she sneaks off in the night to save them.

Web Comics

 * In Elf Blood, Council Captain SKO behaves this way when on-duty, even going so far as to make the childhood friends under her command address her as  when on-mission. Off-duty though, they live in the same quarters, share the same food, and SKO behaves a lot more casually to them.

Western Animation

 * In Recess Ms. Finister turns out to be an old friend of Spinelli's parents. She turns out to be quite cool in the end despite her Stern to Sadist Teacher tendencies.
 * Mr. Ratburn in Arthur who had previously only been seen as a cruel teacher at school. Lampshaded a little by D.W. who thought that teachers lived at school.
 * The Looney Tunes with Ralph the Wolf and Sam the Sheepdog who are friendly to each other before and after the work whistle blows and eat lunch together but are enemies during "working hours."
 * Subverted for humor in one episode of King of the Hill, where Enrique wants to meet Hank after work to get some personal help with some marriage problems he's having. He seems to assume that Hank is less stoic and impersonal after hours. He's really not, but Enrique interprets his actions that way anyway.

Real Life

 * Real Life teachers are often like this, the mix of having to maintain discipline in the classroom and needing to be above reproach in their interactions with students (sometimes to an unreasonable degree.) It relaxes a bit in high school and college, though, as the students get older and more mature.
 * One of the most world-shattering moments in a child's life is running into their teachers outside of school and discovering they're *GASP!* human!!
 * Security guards walk a line between being reasonably personable (even friendly) and being authoritative.