What are inappropriate and personal things you should not discuss in an interview?

Great question! It is very important in an interview to be yourself and not too "robotic." However, being professional and focused is also key. So setting the tone in an interview does make a big difference. My recommendation is to be very professional from the start and let the interview take its course. You will get an idea for the person who is interviewing you and if they crack some jokes feel free to laugh and if you think it is appropriate you can tell a funny story that applies to what you are talking about. For example, when you prepare for your interview think about answers to questions such as :
1) Tell me about a challenge that you had at a recent job and how did you over come it?
2) Tell me about a recent accomplishment and how did you set out to achieve it?
3) What is your biggest strength and what is your biggest weakness?
These types of questions come up a lot in interviews and give you a chance to show the interviewer who you are by telling a personal story or experience.
Never make fun of the person interviewing you, do not tell stories that make others look bad, and if in doubt do not make a joke if you are unsure of the way it may be perceived. Be polite and try to be as honest as possible. It's normal to be nervous during an interview so if you prepare a lot ahead of time this will help when the time comes. Good luck!

Like the others have already mentioned, you want to be sure to be professional.
To be honest, the employers are not going to give you the job based on your personality.
Unless you are applying to be a clown in a circus? :)
(I don't mean to offend I was just using exaggeration to humor)
First and foremost you want to have the fundamental qualities the employers are looking for.
You do not need to take every opportunity to make a joke or play up your personality.
I am sure opportunities that call for humor will arise.
Employers have known to ask silly questions such as if you could be any home appliance, which one would you be and why?

Perhaps, when you first meet the interviewer you can let a little of your personality and humor come through.
Whether that is making fun of snow in April, or commenting on their really nice tie?
As long as you are polite and you don't cross the line you should be fine.
Just keep in mind that the interviewer is not your buddy, so there is always a time & place for certain comments.
Yeah once the interview process begins you may want to get a little more focused and serious.
Plus once you get the job there will be plenty of opportunities to show your personality and share your humor.

Hi Alexander - It's probably a good idea to stay away from discussing your political views during an interview.  

Interviews as always nerve racking but really the best thing you can do is be polite and let your personality show through. There are always standard interview question which you can find online and are useful to review to have a plan of action going into an interview but when I interview people to work with me I want see that they know what the company is and does. If you can answer a question in a way that is related back to the company you are interviewing for it shows that you're interested. This also helps open up the people you are interviewing with and can make the whole thing a little easier.

Hi Alexander,

This is a great question! I think it is important to let your personality shine through during an interview, this can break the ice and allow for a more comfortable interview. With that being said in a professional setting it is important to always 'read the room'. Pay attention to how the interviewer is interacting with you and if you feel it is appropriate. Ensure that you present yourself as taking the interview seriously and prepare very well. Like everything in life it is about balance.