The interaction of Lynsey and Dave is not friendly not kind and not caring. They are definitely not friends. Here is my proof. In chapter four Dave told Lynsey that if she had to shut up for five minutes he head would explode. Dave had just insulted Lynsey and friends don't insult each other. So their interaction with each other is definitely not friendship. Lynsey also insulted Dave she said this: Is your cough all better cause I thought I heard a whiny little voice. And that is not nice nor friendly.
They insult each other witch brings a space between them. Making them hate each other more and more. Later on in the story i think their interactions with each other will change. Because usually in a book the people who hate each other start to like each other. Here is my proof for that one. They had a delay because the principal was there