The "bossy r" means that the letter "r" changes the sound of vowels when in combination with the r. This rap shows how to pronounce the words with the bossy r.
Rufio uses adjectives to insult Peter Pan at the dinner table in front of the other Lost Boys. After some time, Peter Pan stands up for himself and replies with his own, creative insults. This is an excellent example of how powerful adjectives can be in language.