Idiom: Happy Camper; used as a noun
Pete: Hey Chip, what’s going on? You seem to be incredibly unhappy.
Chip: Every time I almost get my work done, someone interrupts me. I’m not a happy camper.
Pete: No kidding, you’ve been quite irritated for the last couple of days. I guess that project was tough huh?
Jean: You’re certainly a happy camper after your trip to Europe.
Matt: I had a chance to visit so many sites and try so many good things to eat. What’s not to be happy about?
To be a "happy camper" means to be satisfied, cheerful or pleased with something, someone, or the result of something. In the first example, Pete noticed Chip’s demeanor and noticed how unhappy he was with something. Chip explains that he keeps getting interrupted. This idiom is commonly used with a negative to mean unhappy.
In the second example, Matt expresses his positive experience in Europe and why he was so happy. He was a satisfied customer, or a Happy Camper.