Let me reword my sentence a bit because I left some things implied but a lot of people didn't pick up on it. It should be an expectation put FORTH in the JOB DESCRIPTION before the employee is hired.
It is a reasonable expectation, PROVIDED the employee knew about the expectation BEFORE he is hired.
If he didn't know about it, and the expectation was sprung on him, then it is UNFAIR.
It is very reasonable to put forth in the requirement:
We are looking for a candidate who can get along with the team. The team likes to party and drink and they all tend to be very young. They do a lot of extracurricular activities together after work. Please only apply if you feel you can fit in well.
No, it's not. The above job description is honest and fair game. Let's not take this into other tangents that have to do with racism or sexual harassment. Be reasonable.
In the US, that would be inviting an age discrimination lawsuit. It's admitting that the company preferentially hires young people (which is illegal), and implying that older people wouldn't "fit in" and would thus be discriminated against.
No, I'm telling you is unfair, unethical, and illegal in many jurisdictions, to ask for the above qualities for an unrelated job (that is, you could ask a wine taster to be alcohol as part of the job. A developer or a show salesman, not so much, and it doesn't matter if it's on the job ad - putting it on the job ad is already icky, and in many jurisdictions illegal).
You can't ethically ask potential employees to "party and drink" for doing a job that's not related to bars and parties, whether it's software engineering or operating a crane.
The whole exchange seems to lack an understanding of the law (e.g. related to age or forcing things like drinking, or even the legality of asking for those things in the ad and/or firing someone who doesn't comply), and even why people would find it offensive and hummiliating. It's all about "but I pay and want a funny partying team", not very far from "but I pay and I want to be able to spit on the face on my employees every morning. If I put it on the job description surely they can't complain!".
Not to mention it's the legal duty to protect employees' health, and alcohol consumption is unhealthy, AND against certain religions AND destructive with certain conditions.
Might as well ask "no muslims", or "no diabetics" in your software engineering job ad.