What does "joke's on someone" mean?

What does "pigment" mean? A color or a pattern, I suppose?

Yes, the word "pigment" is related to color. It refers the natural coloring of animal or plant tissue. In this video, the speaker has used it to refer to the natural pink color of the monkeys around their face and buttocks. Ex: This cloth is dyed with natural pigments. Ex: Humans naturally have varying levels of pigment in their skin, allowing for different skin tones to exist.

What's the difference between "goal" and "objective"? Are they always interchangeable?

The words "goal" and "objective" are often confused with each other. They both describe things that a person may want to achieve or attain but they are not always interchangeable as they somethings can mean different things. Both words speak about the desired outcome of some actions that a person has to do. "Goals" are generally for an achievement or accomplishment for which certain efforts are put. "Objectives" are specific targets within the general "goal". "Objectives" are also often time-related and short term. While " goals are more long term. In this game the long-term "goal" is to kill everyone and not be caught. So, your short-term "objectives" might be to be sneaky and careful. Ex: I want to achieve success in the field of fashion and design things no one has ever designed before. (This is a goal). Ex: I want to complete the sketches for my design project by the end of the month. (This is an objective.)

What's the difference between "lock" and "lock-up"?

"Lock" in this scenario means to fasten or secure something, such as a door or box, with a mechanism to keep it from being opened. Ex: He always locks his car when he parks it. Ex: I can't get inside. The door is locked. "Lock-up" has a couple of different meanings. One meaning is to imprison someone. Ex: He was locked up for stealing. Ex: She's been locked up for over thirty years for murder. Another meaning of "lock-up" means to lock or secure something. Ex: Remember to lock up before you leave. Ex: She locks up the store every night.

What's it mean by "under my breath?"

"Under one's breath" means to speak very quietly, almost so that it can't be heard. Ex: I could hear her singing under her breath during class. Ex: I started cursing under my breath when I saw the news. Ex: He whispered under his breath, "I have to go."

What is the difference between saying "No matter" and "Don't matter"?

Firstly, it is important to know that "don't matter" is a slang, grammatically incorrect form of "doesn't matter". Also "doesn't matter" and "no matter" can sometimes be used interchangeably. Which is how they are being used here. So in this song, they have the same meaning. When using these two phrases however, you have to be careful as they are not always interchangeable. Ex: A: Do you want me to order pizza, or chicken? B: It doesn't matter; they both sound good to me. Ex: A: Do you want me to order pizza, or chicken? B: No matter; they both sound good to me. When choosing between two options, and there is no preference, you will probably hear native speaks use "doesn't matter", rather than "no matter". It is more common to use "no matter" when trying to reassure someone about something negative that has happened. Ex: A: Sorry about your test results. B: No matter – the teacher said I could retake the test.