Best way to capture effect of making people upset? I am an undergrad, I am planning to do some research to see how much I enjoy it before I apply for grad programs.

I am researching the effects of a certain characteristic of a presenter making people upset, uncomfortable, aggravated or displeased during a short clip like a TV commercial. My plan is to have subjects watch a short clip with a presenter and see if they are they aggravated, upset, uncomfortable with the presenter based on that one characteristic changing and compare this across demographics. I do not have much experience with setting up and performing experiments so any help would be much appreciated.

How do I quantify how upset, uncomfortable, aggravated or displeased the subject felt?

How do I make sure that every subjects experience is the same expect for that one factor?

Do I have to do anything special because I will not be able to run the same test on the same exact subject?

I really want to know how to best perform this experiment.
Without knowing exactly what the factor you are interested in is, it is hard to predict how feasible it would be to manipulate it. For example, is it possible to make two videos of the speaker, one with the factor, and one without, with nothing else changing? My guess is that you probably can't do this, so I'm going to focus on how you might be able to run the experiment without that kind of very specific control.

One option would be to make several videos, half of them with the critical factor, and half without. There will be lots of other things that vary between these videos, but as long as the only thing that varies systematically is the factor you are interested in, then you can run an informative experiment. 

You asked: How do I make sure that every subjects experience is the same expect for that one factor? The answer is that you can't really do this. You can try to get close, but subjects will always have slightly different experiences. This is why we need to run many subjects to determine if an effect is reliable. Any given subject may just be tired/hungry/cranky when they come to the experiment and this will affect your results. But, if you run lots of subjects then it is likely that tired/hungry/cranky subjects will be in both conditions, and therefore on average won't impact your conclusions.

Depending on how long the videos are, you could potentially show multiple videos to a single subject, and measure their emotional responses to each one. This is a within-subject design, and the advantage of this is that it controls for some of the random variation (tired/hungry/crankiness) between different subjects in your experiment. If subject A tends to be crankier than subject B, it will introduce noise into your results if each subject only sees one kind of video. But if subjects see both kinds of videos, you can test whether videos with the factor tended to make subjects more aggravated, controlling for their 'baseline' level of aggravation. If the videos are longer, then you could just show one kind of video to each subject (a between-subjects design) but this will probably require collecting data from more subjects to wash out the noise of some subjects being more prone to aggravation than others.