I'm looking for a book from the late 80s. It's about a teenage boy who finds a spaceship out in the country that's crash-landed. There's only one survivor: a boy from a vampiric alien race but he's badly hurt. He's somehow able to show the boy his home planet and the muscular cow-like creatures that his people use for their blood. Eventually the boy's brother, a druggie and Vietnam vet, puts the boy and his alien friend to work making drugs, which they both need masks to do.
Eventually the alien's friends (dressed in skin suits) come to their house. Apparently the boy was a cadet for some kind of interstellar federation, and they want to know what happened. The boy tells them, and an orangutan-like alien (who we are strangely told has the skull of a Hispanic man) and his friends (who are the same species as the boy's friend) ultimately allow him to go with them, as there is nothing for him on Earth after his brother was busted.
The boy is treated more like a talking animal than he is a sapient being because he can't speak the Galactic Lingua Franca, and so when they get to a planet he's taken to be taught and has his brain's plasticity increased so he can learn the language in record time. He's placed in classes with other people from less advanced planets, and he ultimately makes friends with a girl. The girl is an alien from a theocratic planet, and she can unhinge her jaw like a snake's. She eventually freaks out from culture shock, but the boy manages to pass and become a cadet. He also meets a group of humans who were taken from Earth in the 1400s, and who call the alien inhabitants of the planet Devils.
He's eventually given a ship and a partner (whose species looks similar to Big Bird), but they crash-land and his partner is killed by the natives. The boy is imprisoned and tries to communicate with his captives using drawings, but they don't understand him. They're fascinated by his facial hair, as they can't grow any themselves even though they're humanoid, and eventually they allow him to speak to the cameras after he is publicly unveiled. He talks in the Galactic Language and gives them a Reason You Suck speech, but they still don't understand him.